Guys, I'm confused.

My ex and I broke up about a month ago, after dating for a little under five months. Basically, we weren't very compatible. We had a lot of communication issues and frequently misunderstood each other. Because we didn't have much in common, a lot of the time I would stress out over trying to think of things to talk to her about. Every now and then she would accuse me of never talking to her, and this fed into a cycle of feeling almost pressured to perform. Add to that, I knew that I was her first boyfriend and that she was pretty into me, so for a long time, I kept trying to force myself to feel something for her. Granted, I did/do care about her, it just never got to a point of strong butterfly feelings, which always frustrated me. As much as it sucks to say this, I just wasn't really happy in the relationship.

Then BOOM, fast forward to last Saturday, and out of nowhere I meet this really cool girl at a volunteer service day. She's a 25 year old alum from my school, and as we talked, we realized we had a bunch of interests in common. Also, and most strikingly, our conversation was super easy and comfortable. We exchanged facebooks and phone numbers, and are set to go out for a little hiking trip this Saturday.

I'm confused because I feel guilty. As excited as I am about getting to know this girl, I just keep thinking about my ex, and trying to figure out if I'm a bad person for all of this. As far as I can tell, she's still sore about the break-up, but personally I've largely gotten over it. I wasn't actively looking for a new relationship, and was kind of content to just remain single and focus on myself for a while. But damn, if I didn't feel something.

What do you guys think? Am I a horrible monster? Or am I as justified in my feelings as my peers have tried to assure me of?