Hi Lynn,
I was reading your post and Melanie's reply and I agree that you have to start taking care of yourself first! And you shouldn't worry about being selfish, because when you think about it, if you're taking care of yourself, you're better able to feel comfortable around others.
I know this is going to sound very Oprah or Dr. Phil-ish, but no one can make you unhappy but yourself. I obviously don't know your partner, but it does sound like he cares and is not noticing what you're noticing about yourself.
I know it's hard and we all have our own feeling of inadequacies (I'm also 28, and get depressed because it seems EVERYONE is married or at least not living alone - of course, that's not true, but we often have tunnel vision when it comes to these things.)
I also like the idea of writing down what makes you happy...maybe you can keep a journal and write down whatever made you happy that day no matter how insignificant it seems at first.
Well, I've rambled on enough - take care!
:)