Very confused

I don't know what's wrong with me. I've been trying to get over my first ex for over 2 years now and he still plagues my mind every now and then. The questions won't stop coming and I'm just letting myself drown. He's so freaking happy without me, he hates me and thinks I am a nuisance yet he still subscribed to me on YouTube recently. Is it that I just can't let it go? I'm doing pretty well at not stalking him but I feel like sooner or later I'll cave in. And my most recent break up is not helping the situation either. It was traumatic even but I won't go into full details. Does anyone know what I should or can do to stop the pain?