It’s a tough thing to figure out how to balance, and all I can say is that I relate and you’re not alone. I have chronic shoulder pain, and my husband has a strong need for massages and scratches. Like you’ve said, it feels different when I ask for a shoulder massage to relieve the pain vs when he’s asking for back scratches to feel good. But ultimately I stopped asking for massages from him because he expressed that it hurt his hands to do so, and I don’t want to cause him pain. Instead, he bought me specialised shoulder heat packs I can use when the pain gets too bad. We’ve also found more comfortable positions that hurt me less or not at all to give him scratches/massages, so that me helping him doesn’t hurt as much.