I work with my (ex) boyfriend. We have been dating (off and on) for 5 years. We have broken up and gotten back together a couple of times in the past. The last time was last year. Since then we've gotten along well and I thought everything was fine until he just stopped being affectionate with me. We were fine one day, and then he just stopped touching me at all.
I have been waiting for him to explain this behavior, but he hasn't. He is still friendly and calls me, but never explained what is going on.
Part of me wants to demand an explanation for this, but the other part just wants to let it go. I can't believe that he would behave this way without saying anything and I would like to slap him silly.
However, I also don't want to be with someone that would behave this way, and part of me thinks the explanation really doesn't matter.
Should I just tell him to stop calling me and refuse to hang out with him, or should I ask him what happened?

What does "stopped touching me" mean? The physical/sexual relationship has stopped? Were you friends with benefits?

You're in a relationship with him. Ask him. Relationships have ups and downs and you need to be able to discuss both with him.

Yes, I'd ask without confronting him.

You broke up but were still being affectionate with each other?
He probably stopped because he has met someone else, but since you are friends and had some kind of relationship, you should be able to ask him what happened, or you can take control and just walk away.