Being a 27-year-old virgin (pathetic), I'm really not sure what I can add to this conversation, but I do want to say that you have no reason to be ashamed. You're an adult, and you are in control of your own life and your own body. If you like what you are doing, there is nothing wrong with it. You aren't doing anything criminal! And your therapist isn't going to judge you if she is a decent therapist, and it sounds like she is.

It does seem like something you need to work through, as it sounds like you are carrying around a burden of shame that doesn't belong to you. I think you should talk to your therapist about that.