On Tuesday night my boyfriend was out with one of his female friends, they ended up back at her apartment later that night, both drunk, and ending up making out. The next day he told me, and I really don't know how to react. We have been together a year, but only officially dating since the summer. Both of us have been pretty promiscuous in the past, and this is the first relationship in a long time for both of us, but I have no desire to cheat on him, and was never suspicious that he might on me. Both of us ended up crying, with him apologizing and reassuring me there is no one else he loves or would want to be in a relationship with. He just graduated college, and I feel as though he is having a hard time adjusting, and maybe this is something he just had to get out of his system, or was a test of our relationship.
I really do love him, and have been so happy with him, but now I have so many doubts. How will I be able to trust him? I don't want to be paranoid, but he has a lot of female friends, and still intends to be friends with the girl he kissed. Is this a sign he's really not ready to be monogamous/ in a committed relationship, or now that he's done it and realizes we both feel awful, will this be lesson learned?

What are your experiences with this? Any insight/advice?

If he is getting drunk ( or using that as an excuse and you allow it to be OK,) he will do it again and again. He did not just happen at her place, and of course a lot happened at her place and drunk.

If you accept this, it just keeps happening

He went to her apartment after getting drunk with her. He wasn't too drunk to make that decision. No excuses in my book. He's definitely not mature, and I can bet it will happen again.

Learn your lesson he needs to go.

If he is still friends with her and still continues to hang out with his female friends, he is likely to do this again.
I would not waste anymore time on him.

Nobody thinks that he might deserve another a chance? Sometimes you have to make a mistake to realize what a horrible choice it was. He told me right away, and I know it's not a sign of maturity... but neither of us are mature, we are in college and are into stupid things. Does anyone think that this might give us an opportunity to improve our communication and strengthen our relationship?
Its obviously not a good choice on his part and not something I am willing to forgive or forget... but is it not worth trying to repair something valuable rather than just calling it quits and throwing it away?

If you think you are both still immature, then you both should not be in a committed relationship. You won't be able to forget it and you won't trust him again, so why waste your time?

Being drunk is no excuse. He still knew what he was doing. He confessed to you for fear that you may find out on your own. He was hoping that if he confessed, it would show how sorry he is and how much he cares.

Try to repair it if you want but this is likely to happen again, just that he may not be willing to tell you next time. In actuality, this is probably not the first time either.