i have feelings for a girl what should i do?

i have this female friend who i care about and have feelings for. some time ago we went on and it was nice but then we lost touch with each other and when we fond each other she was with some one else. the new guy is nice and makes her happy and i am cool with him so its not like i can be mad cuz i just want her to be happy. i took some time to get in a place where i could see her and not be heart broken and did so. how ever i still have feelings for her. strong feelings. she understands me more ten anyone has. her smile can brighten up my day no matter wat and i'm just happier wit her. se care about me more then anyone has in the past. every now and then i look at her and think if only or wat ifs and then it sets in. part of me wants to tell her how i feel cuz it feels like i have to and also i wanna tel her cuz letting her think i don't have feelings for her any more makes me feel like i'm lying to her and shes the one person i don't wanna lie to. how ever i don't want to tell her cuz i don't want to get in te way of her happiness or mes up our friendship. i think she deserves a guy Much better then me and i don't know if her boyfriend now is that. what should i do?