Do you have any hobbies or passions? In the past I've successfully used my passions to help work through times of horrible insecurity and depression over my job and relationship. I poured myself into art and music and left my self worth in that realm instead of allowing it to be touched by my career and romantic discord. Maybe art and music are particularly therapeutic because they are about expression. But, if you have other interests to pursue I'd suggest maybe trying to have some new adventures with those things. It might be easier to find things to be excited about if they are related to things you're good at or that simply interest you intellectually.

I think I do understand how you feel. You have no idea how much I wish I could comfort you. I hate hearing that someone has made another person feel abandoned and worthless without proper explanation, but that says more about the people who are abandoning you than it says about you. I wish there were a way to make you believe you're special and valuable. I feel that sadness.