Re: very confused...

You are obviously very capable in analyzing your own situation, and have done so.  You knew as soon as you saw his facebook page that you were not exclusive with him and that was a time that you could have faced the situation as it was, and if you weren't comfortable with it, end the relationship.  I'm not really being judgmental - because most all of us if we really look at ourselves have done similar or even greater miscalculations.  

I think that you were really vulnerable when the relationship began because of having come out of intense emotional breakup with your ex.  You have even said so in your post.  What this guy had to offer obviously filled some type of void at the time.

Yes you have a right to be angry, but angry with whom?  Probably yourself.

No, I don't think you are being petty.  What I think you are doing is standing back and assessing the situation you are in and finding that you don't like it.  And hurrah for you!  That doesn't make you crazy and unstable, that makes you rational and real.

My suggestion is that if you're interested in a stable and long-term relationship, you have answered your own questions - and this one isn't what you are looking for.  Loneliness can cause us to do some often irrational things, but you are being very rational.  Finding another caring and supportive relationship may not be quick and easy - like a casual sexual relationship is, and it may even take a long time - if ever to happen, but if that's what you want - go for it!