Hi Elizabeth,
I don't think it's wise to do it behind his back, I know lots of ladies do this, but you need to think about what effect it's going to have on you as a family long term. Although escorting is in no way the same as cheating, it isn't the sex that is the issue here, it's the lies and deciete. You need to ask yourself, is the money worth risking everything for? Because I don't believe it is.
I'm in a relationship myself, but my partner knows what I do, he even drives me to jobs and acts as security for me, but it isn't easy, it does put a strain on our relationship, sometimes he hates it, but understands why I do it, although I know he'd much rather I didn't.
If you feel you can't talk about this with him and come clean, then I would stop. Escorting is fantastic money, but it can be emotionally draining at the best of times, never mind when you're trying to keep it from a partner.
Take care xx