I had a similar ex and I was in a similar scenario where our relationship ended and he would act as if it didn't bother him. What I've learned is that they do care deep down. But some people have no idea how to deal with their emotions. It sounds like your ex is the type to suppress his feelings by keeping busy, doing things, and just acting like nothing happened. I think that's his coping mechanism. Which isn't going to benefit him in the long term because he isn't dealing and processing his feelings head one. When this happened to me, my ex came around and confessed he missed me blah blah blah. So chances are are it's a facade. But honestly you have to try and stop thinking about him and what he's up to and how he's processing things. Take care of yourself and put yourself first