Dear girl who's been replaced,
Just because he's already with a new girl, that doesn't mean you should feel like you've been replaced because the truth is it's impossible to replace you. He might think she's prettier than you, he might think her personality is better than yours, and he might think he's more compatible with that girl than he was with you, but don't let him take away how special you are in your own way, how unique you are in your own right, and how amazing you are in your own light. You shouldn't look at her and feel ugly, you shouldn't compare yourself to her and feel like you aren't good enough, and you shouldn't see how he loves her and hate yourself for it. He might not be able to see what you're worth, but you should know what you worth. He might not be able to recognize your value, but you should be able to recognize what your value is. He might not be able to realize what you deserve, but you should be able to give yourself what you deserve. Sure, he's already with another girl, but that doesn't mean you have to already be with another guy, too. Right now is the time for you to find yourself and pick up the pieces of yourself that were left broken by him. You don't need to be worrying about guys, let alone one who doesn't care about you anymore. I know you're feeling vulnerable, but don't be so quick to fall for the next guy who's there for you because you aren't ready to be with someone at the moment. If he's already happy because of another girl, good for him. He's no longer your problem. He's her problem. Let her deal with what kind of guy he truly is when she eventually finds out. Just focus on yourself, do you, and eventually you'll be the reason why you're happy.
Sincerely,
A guy who cares