I haven't had a lot of long term relationships. The longest one, before marriage, lasted about 3 years. It ended several times.
The last time, I took the clothes I had at Numbskull's house and one other thing: My mom had taken an 8 x 10 frame and put a few pictures of me at different ages into it, and given it to NS for Christmas.
When we broke up, I went to his place, collected my clothes, and I saw the frame face down on his bedside table. I strongly suspected he was already seeing someone else. I may have said, (okay, I snarled) "Already seeing someone else?" and then picked it up and took it. He was saying , "No, no that's not why it's face down. Your mother gave that to me. You don't understand."
Literally, it was all over but the crying. There were things I'd given him, but they were his, to keep or dispose of as he saw fit. I did eventually throw out many, maybe all pictures of him.
I hear you. I got mad at a man I really liked and after not hearing from him for months (he lives in the south in the winter) I deleted the email account i used to contact him, unfriended him on facebook, threw out his phone number, and took the Christmas gift he'd given me outside, set it on a rock, and pulverized it with a hammer. Came back inside and the phone rang, and it was him. It wasn't going to work out, but I do understand the desire to purge.
That's me, though. I don't get to decide what other people do with the gifts I've given them. Those no longer belong to me. Deciding how someone else MUST mourn the end of a relationship, or that they MUST return everything of sentimental value from our relationship is steering my car down their side of the street.