Ah... low self-esteem.
I know it well, Jenn.
I've rid myself of it thanks to a number of things. Getting married (lucked out with my DH), having kids, aging, and therapy.
Aging is the best one. As I get older, I feel more like, "I don't give a damn. I'm me, so take it or leave it."
I feel secure in who I am. I'm okay with not having a phd (although that would be lovely) or a fantastic and fascinating job. I don't feel the need to impress anyone anymore. I like who I am.
I think that in a relationship you have to be willing to give of yourself, and that may mean compromising yourself to a certain extent. But what it all boils down to (and I'm not trying to sound selfish, here) is that it's all about YOU. If you're not happy with what you're giving, then you're not being true to yourself, and the relationship won't be a healthy one.
Besides, relationships come and go. If I were to lose my family tomorrow, not happy with who I am, then I'd have nothing left to go on with. I'm all I've got.
Find out who you are, and embrace that person.
I like what Barb said... "...it's about "growing up" and learning to value yourself, and that has to come from within."