Oh dude, I'm so sorry. Four years is a long time, that's going to hurt badly enough, and the cheating is like salt in the wound.
The first and most important thing to remember is that you're grieving. You're grieving the loss of a relationship, and the exit of someone you loved from your life. Understand that, allow the feelings the space they need to ebb and flow, and be kind to yourself as you go through that process.
Distractions will help to an extent, but you may also feel like nothing is worth time or effort at the moment, and that's okay. Try to spend some time doing the things you enjoy, even just for a little bit each day. They may feel empty and hollow right now, but they'll start to sparkle again in time.
If possible, spend time with people whose company you enjoy. I never needed people around me more than when I was going through a breakup.
Once you're feeling a little better, getting back into dating can be helpful. I wouldn't advise jumping right back into something long-term unless you find someone absolutely magical - but what I found helpful about it was the reminder that actually, yes, there are other amazing potential partners in the world, and I have not lost my only shot at love. That was really healing for me.
Try to hold as fact that this pain isn't permanent. It feels like it'll last forever right now. I know. But the reality is, it doesn't. It fades away eventually, and while it will leave some scars which weren't there before, those don't sting in the way an open emotional wound does.
(Regarding scars; you may find it difficult to trust, when you move onto new relationships. Acknowledge that, be honest with yourself about it and what's causing it, and be very careful not to project it onto new partners.)
Finally, be as kind to yourself as you can right now. You're hurting. Be generous to yourself for a while.
