It depends on what happened. If it was a relationship that didn't end out of anger (i.e. guy was a total jerk the whole time, or he cheated, or something.) and everything ended on good terms I would still wear the jewelry, provided that my current SO was fine with it. I've received some nice pieces. If you can associate it with just the piece itself and no feelings or memories, than I see nothing wrong with it. The only piece I would not wear would be an old engagement ring. I have this kind of thought that like if somebody spent a lotta money on it from somewhere, get usage out of it somehow---either wear it, or have it made into something that you will wear. There are a lot of SO's that are fine with you wearing something that someone else gave to you, as long as you are clear to them that it does not symbolize love or romance in any way, shape, or form and that you just like the piece or brand. (I had controlling ex's in the past, one or two of them who would never allow this type of thing because of how they are. But my current SO wouldn't mind.)
However, I am very non traditional. I also don't believe it's right to give any gifts back to your ex that he might have given you, and I also would never want an ex to give any of the pricey gifts that I gave him back to me. Me and SO spend an equal price range amount on all of our gifts so it just wouldn't feel right. If something happened and we broke up, I would kind of be offended if he asked for any jewelry back or if he was like, "Give me those earrings back from Christmas." Then I would be like, "Uhmm should I ask you to give back your fancy watch that I got you for Christmas? It's the same price range, except I don't expect people to give "gifts" back, or it's more like borrowing and not a real gift." It would just feel weird. Like kind of childish or something. Like what would you need it back for? Lmao. To give to somebody else, because that's tacky and not fair to the next girl? Or to sell? Ehhh, a gift is something for the other person to have the choice the keep---guy or girl, whatever side. When I hear of males and females asking for gifts back, it registers more as borrowing an item for some reason. Not very nice.