I'm thinking of wanting to hook up with my ex
Why do you wan to do that?
Because the sex was always great, and I miss it.
Hey, we all like great sex, but you should probably move on from this relationship. You will just get stuck in a rut if you can't move on.
Screw that. I want to see what she's like now.
While it's fine to see how she is doing, I believe you really shouldn't take it too far. You two broke up for a reason, so why not move forward and learn from this relationship? You never know if the one is actually right in front of you!