He bought me a ring..

So I recently broke up with my boyfriend of almost two years as I discovered that he was seeing a few of his ex girlfriends on the side (whilst I was sorting out finances for the apartment we were planning on buying together!) and I’m trying to sort everything out.. he bought me a pretty serious ring, kind of like a low-key engagement ring (he didn’t exactly do a full on proposal) and I don’t know what to do with it... do I sell it? Give it back to him? What do I do 😓