Guy friend I like, sleeps with other girls?

I met this guy when both of our best friend introduced us. They have known each other their whole lives. I started talking to him because we have one of the most important things in life in common. So we start talking I start getting utterly pissed at everything about him. First of all he is a womanizer, drunk, smoker, complete *** basically. Complete opposite of what I am, or want.

So while I'm ranting about my best friend for something bad she has been doing for a long time. We just start talking about the most random things. I still dislike him after all this because lets face it who changes?

Then my best friend tells me he is going back to school. I really don't think too much because everyone needs an education. Then he moves back to his home town. STILL think nothing of this until my best friend tells me that he is going there to apologize to his family, and on the way back to break up with every one of his girl friends! Then he moves back & shortly after he goes to visit his mom & she gets shot by her boyfriend. So I'm still talking to him this whole time, and then she dies. A few weeks after that he emails me & tells me that he has indeed has his first child.

Then he adopts his younger brother & sister. While he is supporting them, he is also homeschooling himself.

On Valentines Day he emailed me & asked me if I would be his Valentine. And he told me he really liked me. And that he DID NOT want to start anything online, I realized ( yeah kind of saw it coming!) that I really like him too. I agreed that I did not want to start anything either.

We keep talking keeping it friendly.

You might have seen this one coming but then my best friend tells me that he has been trying to bring girls home. TO HIS BABY! HIS BABY GIRL!

Honestly I don't know what to say to him. I can't talk to him anymore without feeling like he is just lying to me. I just feel like I should have seen this coming, and feel like a complete idiot.

So should I feel this bad about what is happening?
What should I say to him?
Should I just leave it at friends?