Is this she a relative : sister, aunt, mother, cousin, daughter, grand mother 🛑? If yes suggest you do it if his doing that really offends you that much. If the person is an acquaintance, a client, or friend who pays for a professional shoulder rub back off.
If it is another female trying to capitalize on his good nature and disrespecting your relationship you should ask your boyfriend to decide whose shoulder he wants in his life. Nothing further is required of you. It’s his choice. Don’t engage with the female it’s beneath you.
I would say kick her ***** @$$ but no dont