Do I have a right to be annoyed and upset with my housemates?

You're seeking validation for being upset at a perception of being passed over by your group of friends for this 'newbiie'. I think that's quite a natural reaction to the situation as you've described it. However, it was you who said that you didn't want to live with the group if this sixth person was there also. It sounds to me a little like because they were originally your friends and this sixth person was an interloper, you expected them to agree to your demand that he not live with you next year and when they didn't do this you felt angry and aggrieved. It's a little as if a bluff has been called.

I understand your emotions regarding this but I can also see that if these other four flatmates have all decided that they want to live with the new person they probably feel that the only way forward is for the one who doesn't want to live with him/her lives separately. That's going to seem a little unfair to you, but is practically possibly the only way forward.

But he has other friends he could share a house with next year whereas I don't so since the housemates side with him it'll mean I need to move back home so the social life I've tried hard to build this year will be destroyed because of my housemates since I will need to drop the societies I have started. I think that is a legitimate reason to be angry and upset. I would've expected my best friend to side with me since she constantly tells me how important our friendship is to her but that's clearly a lie since shes willing to just let me live on my own.

You have 2 options, put up with the guy and live as a 6, or act like a child and move home.

Sounds like you've burned the bridges already though, and asking for reassurance after the event doesn't seem like as good an idea as asking for advice beforehand.
In any living situation there will always be people who don't get on, but you've acted in a way that has left you without a place to live.
You wanted to throw him out on his ear, and look where it's landed you.
Whether he has other people to live with or not, doesn't matter, he, and the other 4 people you live with, want him to leave with you all. So you now have no where to live because you couldn't act like an adult.

You have 2 options, put up with the guy and live as a 6, or act like a child and move home.

Sounds like you've burned the bridges already though, and asking for reassurance after the event doesn't seem like as good an idea as asking for advice beforehand.
In any living situation there will always be people who don't get on, but you've acted in a way that has left you without a place to live.
You wanted to throw him out on his ear, and look where it's landed you.
Whether he has other people to live with or not, doesn't matter, he, and the other 4 people you live with, want him to leave with you all. So you now have no where to live because you couldn't act like an adult.

What you're saying here doesn't really have any meaning. You're just throwing about the word "child" as a pejorative to try and invalidate anything the OP has to say. Additionally, a lot of what you have to say isn't supported by anything that you could know as fact.

There's no reason to think that in any given situation leaving a place where there's conflict is inidicative of acting in a childish manner. That's just something you've chosen to say because it has a negative impact.

Yes, and this is why I can understand your feeling upset and sidelined.

Have you tried calmly taking your best friend to one side and explaining all this to her? Does she know just how much this has upset you, and how much you feel it will affect you next year? Alternatively, if this is the group decision, is there no way you could put your differences with this other person to one side - surely if that meant living with your current friends and not having all the upheaval you mention it would be better overall?

How am I acting like a child for not wanting to live with someone I don't get on with? I didn't want to throw him out on his ear since he has other options whereas I dont

I'm in my second year of uni and there are 6 of us sharing a house. Originally it was only supposed to be 5 but someone joined last minute because he didn't have anywhere else to go. I didn't want this to happen but there was nothing I could do about it. Anyway me and this other guy don't get on well and since the house has started talking about living arrangements for next year, I have said I't best if me and that guy don't live together. All of the other house including my so called best friend said they want to live with him and I am left on my own which means I will need to commute from home next year since there is no one else I can live with. My best friend said it'll be ok since she will make the effort to visit me but I don't think that makes up for the fact they're practically kicking me out on my own. Do I have a right to be angry and upset with my housemates?

What you're saying here doesn't really have any meaning. You're just throwing about the word "child" as a pejorative to try and invalidate anything the OP has to say. Additionally, a lot of what you have to say isn't supported by anything that you could know as fact.

There's no reason to think that in any given situation leaving a place where there's conflict is inidicative of acting in a childish manner. That's just something you've chosen to say because it has a negative impact.

Would pathetic be a more appropriate word? Thinking your friends are going to back you throwing someone out the house isn't a normal assumption to make, especially if you're the only person who doesn't get on with him? The other 4 housemates invited him to stay there, and now OP wants them to side with the decision to throw him out?

Was always on to a loser. Made a gambit, it didn't pay off. Accept the consequences.

It was only 2 of the housemates who decided to let him live with us actually and like I said before I'm not throwing him out. It'll be next year when we all move out of the house anyway. It's not like I'm saying I want him out now. He has somewhere else to live since he has other offers whereas I do not. I don't see how its pathetic to want to continue living with my friends

You can continue to live with your friends, but it sounds like you've made a him or me statement, and they're all now siding with him.

That's the pathetic bit, is laying down an ultimatum.

How is it pathetic to not want to live with someone who I really don't get on with. It might help you understand better if I tell you why I dont like him. He uses my things without asking, he has broken some of my possessions then had a go at me when I asked for the money for them. He is practically always on drugs and he never cleans up after himself even when everyone tells him to then goes behind my back to complain about my attitude to other members of the house. Thats why I don't want to live with him for another year.

I've not said it's pathetic not to want to live with him, it's pathetic to issue an ultimatum and then get upset when that doesn't go your way. That's the childish bit. You can't demand he doesn't live with you all next year when the other 4 people get on with him. If you'd said "this is what's going on, I don't think I can live with him next year if he carries on" and they've just said "we'll miss you" then that's a bit *****y, but if you've been more blunt and just said "he needs to go" then I can see why they've sided with him. Your original post makes it seem like you were very blunt, hence my lack of sympathy.

I'm in my second year of uni and there are 6 of us sharing a house. Originally it was only supposed to be 5 but someone joined last minute because he didn't have anywhere else to go. I didn't want this to happen but there was nothing I could do about it. Anyway me and this other guy don't get on well and since the house has started talking about living arrangements for next year, I have said I't best if me and that guy don't live together. All of the other house including my so called best friend said they want to live with him and I am left on my own which means I will need to commute from home next year since there is no one else I can live with. My best friend said it'll be ok since she will make the effort to visit me but I don't think that makes up for the fact they're practically kicking me out on my own. Do I have a right to be angry and upset with my housemates?

No I didn't mean to sound blunt. What I said was I can't live with him if he keeps doing this. We've had meetings with him but nothing changes and thats what I told my house I can't live with him for another year when he's like this and they've basically said "goodbye" to me.