Should I just act as if it never happened?

I started talking to this dude and 2 months late we slept together for the first time. Afterwards it got weird, he wasn't talking to me, wasn't answer my texts or phone calls, and just ignored my presence.

I later find out from his brother that he was in a four year relationship with this girl and they were engaged. Well he went out of town on business and she cheated on him and got pregnant. They were only 3 weeks away from their wedding and everything! So she left him for a baby father and that was that.

Well me and started to become more involved and still sleeping together, but still not in a relationship. And I start to have feelings for him, but then all of a sudden he starts acting weird and I'm like what's up and he wouldn't tell me. So I got creative and got him to trust my friends and give up the goods.

So he does and I find out that his ex is back in his life. Her babies father has left her and so she comes crying to him, because he is a sucker for her, about how he left her and she now realzes that she messed up and all that crap. So basically while he's in school he is letting her stay in his apartment which he pays for and pays all her baby bills and things. He is taking care of her and her child while he's in college doing his thing, which is 2 hours away.

He hasn't been man enough to tell me whats up and I don't know what I should do because now my feelings are invloved and I don't want to let go but everyone keeps telling me I should. What do you think?