My crush is dating someone, what do i do?

Hi, this is my first post here.
I like this guy for a while, we met nearly a year ago, he wasnt dating her at the time, im also a friend of her, i dont know what to do, my heart really hurts when theyre talking, when he talks about her, im jealous but i dont want to ruin their relationship or the friendship i have with them? what should i do? should tell him? pls respond or give me tips! anything! i really dont know what to do . . .