Should I break up with my boyfriend?

Polyamourous is just a fancy word for being a whore. I don't understand people who think like you, it's disgusting.
Sorry, just my opinion XD

This is a nasty mindset. As long as all of the people involved in the relationship are aware that it is polygamous there is no issue. And whilst polygamy seems weird to you, monogamy seems weird to others. Just let people be happy

Warning this thread is really long and long winded I just don't know how much context to use to I tried to cram in a lot of it.
I'm only 19 but am in a serious long term (5 year) relationship and lived with my boyfriend for a year before moving to university which is the other side of the country. I love my boyfriend but for about 6 months leading up to university I had small infrequent thoughts wondering if my relationship would last while at university which were followed imediatley by guilt and pushed at the back of my mind. These were because I would get mad at him for no reason and want to go home but usually ended up going back to him the same night or next morning because it was better than being home with my family. While with my boyfriend I ended up pushing most of my friends away and only spending time with him. Over the past year and a half I made a conscious effort to spend more time with friends but that was only about once a month.
After moving to uni I made an effort to make friends and go out more. I think the combination of becoming more independant and the copious amount of male attention I recieve has really boosted my confidence and whereas back home I appeared quite outgoing but suffered with anxiety when trying to talk to people now it's no longer an act. I barley get anxiety at all now. I think I prefere who I am now.
I felt guilty for not missing him when I didnt see him for 3 weeks but put it down to keeping myself so busy. He visits me fairly regularly now but is absolutley miserable without me. He's extremly sweet and loves me more than anything and really doesn't deserve me to feel like this. He rings me in the morning to wake me up for lectures so I dont miss them, he sends me gifts, he offers me emotional support and is always there for me. Part of me feels like the main reason I love him is because he loves me so much. He's also the only person in the whole world that I trust and I think he understands me more than anyone. We still have sex a lot when he visits and have an exciting sex life and he always makes sure I finish first yet I still don't feel satisfied. I slept with another guy since starting uni (frst time ever and with my boyfriends permission) and didnt enjoy the sex then either but I think that was down to the other guy being bad in bed. The only way I can think of describing my feelings towards my boyfriend is as if he was my brother. He's been such a big part of my life and is in nearly every memory and photo I have since I was 13 so no matter what happens there will always be a connection between us. I'm really close to his family and wont be able to get rid of all the stuff he bought me and all the photos of us because almost everything would remind me of him, and he's even in most of my family holiday photos. He's my best friend and loosing him would break my heart so I think I may be staying with him as a lover so I don't loose him as a friend. I've agreed to get a house with him next year and share a car so feel more pressured than ever to make a decision as to where this relationship is going because if I decide against once we get the house I'll be trapped.
I havent given him any indication that anythings wrong in the relationship and have even discussed marriage (We're engaged) and children with him so this would be such a hurtful shock to him. I really dont know what to do and need advice. I don't know if this has been partially brought on by not being able to talk to him about much of my uni stuff as he doesn't understand (there has always been an intelligence gap but it felt less important when I was young) or by my attraction to other guys I'm meeting here although the main reason is that Our relationship has started to feel like that of siblings. I think If we were to split up I would become polyamourous as I've always been poly-minded and want to stop having to push away and hide my feelings.