Engagement ring meant for his ex

So my bf and I are discussing marriage. We have a daughter together, also live together and have been together for 3.5 years. He has an old engagement ring that he was going to use for his ex when they were in their mid 20s (my bf is now 36). He asked if I would be ok using the diamond for that ring? I feel like I would be but idk if things would change once I got the ring. To me it’s pointless to buy another one bc the ring is exactly what I want. A round, diamond, 6 prong ring. The ring is gorgeous. I told him just to reset it bc I don’t like how far it sticks out. Am I crazy for this or would anyone else consider this? To him he said it doesn’t remind him of anything then again he is not a sentimental type of dude at all. He would also buy the band I like and like I said reset the diamond. So pretty much the diamond would be reused. The only reason I am considering is bc it would be a new setting and band. Basically same diamond bc I love a solitaire and that’s what this ring is. Now if it as a princess cut I’d say hell no bc I hate the style. But why buy another diamond? That’s gonna look and be the same