The vibe you get might be that he finds you attractive, but that doesn't mean he will leave his gf for you. (It is possible to be attracted to other people when in a relationship. It doesn't mean anything except that he's human.) OK so you like him. So what? You said you won't tell him and you won't quit, so just keep on living your life. Find some hobbies, hang out with friends, date other guys. Either your feelings will eventually grow less, or you'll meet someone you like more, or he'll leave his gf and maybe you'll have a chance to date.