I love my best friend...

I'm a girl (bisexual) and I really like one of my best friends. He already has a girlfriend and I would NEVER do anything to break them up but it's really aggravating to see her every time I'm around him. She doesn't even really like me that much and from what I can tell, she doesn't really like him either. He's asked her out on several dates (just them 2) but she's rejected him every time. They've only gone on "dates" with groups of friends, which I guess I understand if that's what makes her comfortable... tbh not really. I know you're probably gonna tell me to suck it up and deal with it and life sucks, but I just figured I'd ask anyway. Should I tell him how I feel even though he has a girlfriend or just keep it to myself? Please help.

Keep it to yourself. He likes her and does not like you in that way. You are friends. This is his prerogative.