im not saying to give up on the relationship...just get some space while you can...before you are married...
im not sure how old you are but if my 22 year old daughter wanted to move in with her bf i would be against it...i am 48 and was married for 17 years...then divorced...then met a guy and after 4 years moved in with him without being married and we have been living together for 4 years now which i now regret..there were promises made that have never happened....because i believe in marriage and now dont know if it will ever happen..
Forecasting the doom of your relationship in the heat of an argument doesn't accomplish anything. Why don't you two try couples counselling? It sounds to me like these arguments are starting from misfired signals. Why not work at sorting out what causes these arguments rather than just give up? There's a lot of things you two could do together (books on anger management, communication, etc.) before calling a break.
IMO coming home in a bad mood and then expecting your boyfriend to bear the brunt of it isn't a great loving tactic to dealing with a bad mood. If you're in a bad mood, let him know and then back off until you've dealt with it. Don't put the pressure on him to "fix" and make your emotional world perfect. I'd also recommend that once you see one of your typical arguments starting, to walk away. Don't try to resolve it until you've both cooled off. Choosing to stay and continue one of these arguments will NEVER help your relationship. If anything, it'll just become a contest of pride, and as you've described, when you've run out of valid things to argue about you'll start projecting these problems into your future. I think you both need to learn to walk away when you're too upset to talk reasonably, and then be willing to talk about it only when you're calm and about to think rationally.
get your own place...give yourselves the space while you can...and let time see what will come next...don't move in with him the way things are...take it from me...i have been there...
I don't think it would be a step back if it means salvaging a relationship. Maybe the break might be good for the both of you. Maybe you will learn to appreciate each other more when you are not on top of one another. It doesn't mean you can't ever live together again but take this time for yourself. Get some space when you need it and when you do see each other you will enjoy it rather than argue. Good luck.