It's okay to go on FB and look at his stuff. But don't assume that it is a girlfriend. The best advice is to ask him what his relationship status is.  :-)

Hey girls!
I'm dealing with a weird situation with a guy and I would love to hear your opinions about what I should do.
I met this very handsome, sweet, funny guy while I was abroad 3 weeks ago and ae clicked perfectly, I remember people asking if we were a couple more than once, hehe, but we were both very shy and nothing really happened, although there was a lot of tension between us. I have him on Facebook and we haven't talked until 3 days ago, when he messaged me because he saw on the news that something terrible had happened in my country, and he wanted to make sure I was okay (I think it was an excuse to start a conversation). After 3 days he stopped replying and I did this terrible mistake of stalking his profile, and what I found out is that he MIGHT have a girlfriend (you can't really tell if they're a couple or good friends, really). I know I shouldn't have stalked his profile, and now I don't know what to do because I really want to try something with him and use PW and BWD with him, but I don't want to interfere between a relationship, but then again, I don't even know if that girl is his girlfriend or not.
What should I do? Should I still use PW on him? I really want to be with him but I don't want to cause harm to anyone..