That's a tough place to be and one that I think a lot of us have been in. Rather than focusing on the things that you don't like about yourself try focusing on the things that you do like about you. It's a hard thing to do to begin with but it does get easier over time. Also believe it when someone gives you a complement (most of the time there isn't an alterior motive for people to complement you). Yet again easier said than done I know but seeing yourself the way others see you is often a good thing. We are generally our toughest critics.
What worries me about your post is that you think that there is someone who only wants to be with you to make someone else happy. Have you talked to your husband and the other woman about this? What do they say?
I hope that you feel better about you soon. Take care