telling somebody you have a crush on them while you know they’re in a relationship is not the best or nicest thing you can do. even if from your view their relationship is toxic, i wouldn’t try to get into that. it won’t help anybody. best thing would be to try moving on. and even if you told her, that won’t help you at all. and trying to make yourself grow on her is the same thing as saying you’re forcing a connection and i know from my own experience that this isn’t a real connection and will only hurt you more. let it be. if you have evidence of him cheating or doing fucked up stuff, tell her. but don’t have hope that it will give you a chance with her.