Confused And Concerned About Situation
Let's review your boyfriend's behavior: gets drunk, ditches girlfriend, gets completely shitfaced back at shared home, bitches about girlfriend to drunk friends, makes out with another woman-who happens to be married to another friend-while his girlfriend sleeps in the next room, gets caught, blames girlfriend.
To me, that looks like someone slamming his hand down on the eject button, i.e., he wants out of this relationship. Which means your willingness to stay in this relationship-if "this chick" comes through with the apology you feel she owes you, if your boyfriend corrects the record and quits boozing-may be irrelevant. Because if your boyfriend wants to dump you but lacks the decency, balls, or self-awareness to end it himself (it's possible that he may not be consciously aware that he wants out), CACAS, he'll keep pulling stunts like this until you've had enough and you dump him.
I could be wrong, of course, and I've been wrong in the past-see "clitoris, location" and "male bisexuality, existence of"-and this is advice not binding arbitration blah blah blah. Maybe his behavior can be attributed to a crazy meltdown reaction to his ex-girlfriend's death. Clearly, his feelings for his ex were more complicated than he let on. I'm thinking he still had feelings for her, CACAS, and I'm betting that she dumped him. He may have said only shitty things to you about his ex because he thought that's what you wanted to hear. Reminding him about all of the shit he talked about his ex may have made him angry with himself, and he projected that anger onto you, and now, in the cold/sober light of day, he'll be able to see that and he'll apologize and you can rebuild your relationship.
Or, you know, not.
My uncle died in a car wreck. I didn't know him well, but we lived in the same city and he named me executor of his estate. He was single, childless, straight, unmarried, and-as it turns out-pretty kinky. I've been looking around online, and some of this stuff in his "playroom" is worth a lot of money. But you can't haul a $1,000 bondage table out on the lawn for a yard sale (at least not where he lived). So what do you do with a dungeon full of BDSM gear when the owner dies unexpectedly?