Look, your boyfriend is probably a terrible slob, and too lazy to even clean up his apartment for your sake. He means to get to it one of these days, but then he starts surfing the internet again, or playing with his Wii. He is worried that if you see his place now, in its natural, untamed state, you will be revolted and dump him. Just call him out on it and give him a deadline or something. But telling him that you're going to a party without him is a whole different thing, and will make him think that you're going to cheat on him. Don't do that again if you want to stay in this relationship.
Good decisions come from experience. Experience comes from bad decisions.