What should I do?

Me and my boyfriend have been going out for 81/2 months now. And on our 1st month i cheated on him with my ex cause i still liked him. And now i really regret it but i dont talk to my ex. One problem is that we get mad at each other alot..the other is that i'm making steps for one of my friends quinceanera and my ex is in it. Well i told me boyfriend and he got mad and he said he dosent' want me near him(so he doesn't want me to be there but i can let my friend down cause i already promised) and he even said he dosent trust me if hes there. And i understand him but i did that when we bearly went out and now that we've been together for a long time don't you think he should trust me by now? I mean at least i told him right? Isn't that good? well i really don't know what to do...opinions please? ooo and as you can tell he's a lil "hardheaded" so hard to get to him when you're tryna change his mind lol