What might be a crush

I don’t even know if I would call this a crush but I’ve always had a thing for this one guy, he’s starting to see one of my good friends sisters, and I don’t know if he actually wants to be with her. Keep in mind he hasn’t have an idea that I have a thing for him, and I am honestly happy they are happy, he just doesn’t seem into it. This girl I talk to sometimes, and she’s an angel. But if he doesn’t feel it and ends it (after I wait a few months or weeks until I know he could be ready for something) should confess my feelings or don’t because he was with her first?