found out my "fiancé" is cheating on me.

It's a really long story. But I got solid proof he was lying to me and cheating on me for who knows how long and he was heavily on drugs while doing so without my knowledge. It's the breaking point so there's no going back. We've been together for so long that's the person I planned on spending the rest of my life with! We have no children together, thankfully so I'm just wondering for anyone who went through the same. How do you cope? And what do you do to get your mind off of it? Just looking for some words of encouragement in this really awful rough patch of life I'm going through!