If we go by the Jimmy Carter standard, then you've already sinned the moment you've lusted in your heart. So I'm going to say that the answer depends on how you and the masseuse perceive the transaction. Sensual, and she's a masseuse, sexual, and she's a prostitute.

I got a massage from a sexy Thai lady in Bangkok once. She was sexy and feminine, with big fake tits. She told me to get naked under the towel and then she oiled me up and started massaging. At first I thought it was going to be a normal massage, but then she started brushing my cock and balls until I was rock hard. Then she told me to roll over and she'd do my back. For some reason she put a towel over my face so I couldn't see, then I felt her weight come down on top of me. She reached around and stroked me off while she stuck her finger up my ass. At least I think it was her finger?

Never cum so hard in my life. Best $10 I ever spent.