What's the best way to stop seeking approval from others (especially romantic others) and start giving it to yourself?
For me, I work hard to be a person I'm proud of being every single day. I get shit done, I take good care of myself, and I try to be awesome to others. I basically make it really hard for me not to like myself.
Then, when someone doesn't like me, especially romantically, I think any one of four things: 1.) Really? Dude, you're an idiot, 2.) Well, you must want something other than what I have to offer, in which case I wish you the best and hope you find it, and though it sucks that we aren't compatible, it's for the best that we know so we don't waste our time trying to make a fit where there isn't one, 3.) Too bad you're jealous and/or insecure, or 4.) You must not know me very well yet, and in time I'm pretty sure you'll come around on some level.
Meanwhile, keep on doing the things that make you proud of yourself. Tackle and finish projects that you're proud of, learn a new skill that you think is really badass, treat your friends well, and get rid of negative people in your life. Fuck those who don't approve of you. And know that anyone doing anything remarkable is never going to get everyone's approval across the board.