Self worth depends on how another sees me

I have just realized that the way I see myself depends on how my ex sees me.He was my friend for years then my first.He ended it without reason.We now are friends..kind of.But I only feel good about myself if he is nice to me or says something that makes me think he sees me as fun or pretty.I have tons of people who tell me how great and pretty I am..but if he doesnt feel that way i feel I have to prove it to him.He is the only person in my life who has ever not wanted me.I ended up saying something really embarassing to him the other night and now I feel even worse about myself.How can one person make me feel so crappy when I have everything else going for me? Help please!