I have feelings for my friend's boyfriend, what should I do?

Ever since this handsome, funny guy started dating one of my friends, he’s attracted me. Both physically and the way his personality clicks with mine. They’ve been going out for almost 2 years and have lived together for a while. Every time I’m at their house I sense chemistry between us. Also when we’re out together with others he’s affectionate towards me. I know they’ve had a rough relationship recently but they’ve decided to try harder. He’s started messaging me recently after asking for my number, so I know he feels something towards me.

I guess it’s an impossible infatuation since I know it will ruin a friendship…even if they were to break up in the future.