getting close to someone

I met someone who I was starting to like.  We spent many hours together talking and hiking.  We finally kissed and became somewhat intimate... my feelings grew for him.  Then he told me he's been in correspondence with a girl-I asked if they had been romantic and his delayed response told me they were and he admited to it.  Honestly, I thought he would have said something before we were intimate.  Anyway, that was a trigger for me of not being good enough, not being special. I just feel so alone.  I know it's not true, but, I feel hurt.  What's worse is that this guy, who I should never even see any more, is still on my mind and I want to call him.  I sent him a text a few days ago just saying "hey"...he never responded.  I guess that was his response.  So today, I'm dealing with my actions of not clarifying that he was single before being with him and I feel like such a fool...plus, i miss him.  Again, I'm so grateful I have a place to come to share my struggles and hopefully help others.