hindsight is 20/20, but you're not. No worries though, glasses are 'in'

 Stop trying to impress him. He's not worth it. It takes a lot longer to get the pieces of yourself back then it does to give them away.

 Stop worrying about what everybody else thinks of you.

 If he loves you, he will come back. No matter how much you fight, how much you cry or scream, he will only come back if he loves you. There's nothing you can do about it. So sit back, and wait for time to make him miss you, or time to make you see you're worth more.

 Being a father doesn't have to mean biologically. Give your step-dad a chance, and when you do you won't regret it. He's more of a man than your sperm donor ever could think to be.

 I wish you hadn't changed.

 Don't change a thing. I know you're miserable now and you wish you could change absolutely everything, but if you could see me you'd know that you'll lose the weight, you'll travel the world, you'll get the guy, and everything works out in the end.

 It will get worse and she'll completely break you. She'll never be yours and you'll always love her. But don't worry, eventually things start to improve. Accept yourself, everyone else will do.