Should I let him get away with it?

I met a guy at the end of the summer and we have been dating for the last few months. Things were going well at first, but then a few weeks ago he became a little distant. For example, he wouldn't return my texts sometimes, and he stopped making plans with me in advance and instead he would just wait until I asked him to do something or would call me at the last minute to hang out. I started to get the feeling that he wasn't really looking for a super committed relationship, which was OK with me because he was fun to hang out with and I enjoyed his company, at least for the time being.
Then today I found out on the Facebook page of one of his friends (he and I are not Facebook friends, which I always thought was kind of odd) that there is a girl who lives down South that he appears to be dating as well and has been for quite some time based on the pictures I ended up finding. Pictures going all the way back to last fall.

Truthfully, I am not that upset since things haven't really been great for the last couple of weeks, but I am torn on actually even telling him I know about the girl. I am thinking it may be easier to just stop responding to his texts/calls. At the same time I don't want him to think he got away with being a cheater.

– Cheater, Boston

I'd take 10 minutes and end the relationship. Not just because he's a cheater, but because I believe in clarity. Just say (over the phone or in person), "Hey, we've obviously been growing apart -- and I get the sense from your behavior (and the internet) that you don't want to be in a committed relationship. It's time for me to move on."

He might disagree and try to keep you around, but you can handle that conversation. It just seems to me that you've been doing a lot of guessing. I find that talking it out – even if it's just to break up – is more helpful in the long run. I don't believe that people learn much about themselves and their relationships when they simply disappear.

Readers? Should she have a breakup talk or just stop responding to texts/emails? Is she making too many assumptions about the Facebook findings? Is it weird that they're not Facebook friends? Discuss.

– Meredith