Agree. Keep him paying as long as he comes. Even if you are tempted baaadly. Some of them just waiting for freebie. I had one like that just recently. He believed, that because the sex was awesome (and was), I shouldn't be charging him, because 'I wanted it too'. No comments.
As per sub experience - I know your pain. I am sub myself, and I know how difficult is to find a suitable lover. I do not offer BDSM in my menu though, only if I see that somebody could be into it, and I know him well. However submissive nature helps in this job, at least this is my case.
Ping me on priv, I might be maybe able to help:)