Suppose that he was living at your place and when he breaks up, he leaves bags of his stuff behind.
What do you do?
The best approach is to contact him and give him a deadline: a couple of weeks to a month is usally reasonable.
Say something like:
"You still have a couple of bags at my place - As you can imagine I don't really want this stuff around... Can you pick them up in the next couple weeks? - I would appreaciate that - Thanks!"
If you don't hear from him, send him one last reminder and after that either get rid of it or bring it to one of his family members or friends.
You warned him!
It's his stuff, not yours!
He is the one who should be taking care of it!
If he doesn't care, neither should you!