Let's break this down:
hi, so me and my boyfriend tell each other to shut up all the time right, - You shouldn't really be doing this to start with.
and this morning he kept farting so i was like can you just go in the other room (there was other people in the house) - Whilst disgusting, it's better out than kept in. Completely get why you said to go to the other room, or suggest the bathroom with window open.
so he said shut up people are asleep, so i went into the other room. You did say at the start that you both tell each-other to shut up on a regular basis, so he probably said that as if things were normal / banter conversation like you always have.
woke up a couple hours later and he comes in asking for my earphones, Surely he has his own?
and i was like, don’t tell me to shut up, You also say to him 'Shut Up' at times (quote from your original opening line 'hi, so me and my boyfriend tell each other to shut up all the time right'), so you should have said to him 'What I said earlier was accurate, you shouldn't be constantly farting in bed with me or anyone. Go to the toilet and sort it out'.
and then he said you tell me to shut up all the time, so YOU don’t tell me to shut up and i said OKAY, but i just told you to not tell me to shut up and then he walked out the room - unnecessary argument here that was technically started by him saying 'shut up' first, but you shouldn't have followed it up by the snarky comment 'don't tell me to shut up', given you both say it all the time.
telling me i’m “boring” and then he texted me saying “you need to sort your attitude out because i’m starting to lose interest in you” and then went on to call me “stupid” and “entitled” and how i should “get over it” - he farted. That's normal for us all as humans to do. To over-exaggerate it and turn it into an argument is stupid, so I get why he's frustrated that you're making it such a big deal. It's not.
i get that i probably should have established at the start that we should both stop telling each other to shut up - that would have been ideal.