That it sucks. And that it is base. But it's weird. It's like this cold bucket of water.
Whatever people had before finding out about an infidelity is forever changed afterwards. There is no going back to what was before. That is dead. Now there is only future. It's almost clinical with me. All emotions get severed. There isn't any gray area. I don't believe people change in this regard. If someone cheats, it's in their nature and it will repeat itself.
If they are the one being unfaithful - then they are weak and meaningless. It is a sign of untended business, in my mind. There was an opportunity to handle things the right way - and that time has passed. The infidelity was the way the person chose to handle delivering the news. To be found out instead of handling things head on.
I realize that I sound as if I have been terribly wronged at some point, and sure I've been cheated on in my life - few haven't - but I don't have any real scar from it. I'm no victim. It didn't overwhelm the makeup of who I am. I don't even really get that worked up over discussing it. Because it is just so basic. It's like describing a color. I know what my representation of that thing is. I have no questions about it but I'm sure I'll see different variations of it to come in my life.
For me, this is life's way of telling you to turn the car. You are an idiot if you don't. You are destined to feel the same pain over and over again until your character decays or you break your own soul ... or you simply make the change that is necessary.
Move away from that person.