Don't tell her and don't end your relationship.
Instead, ask yourself why you did it? What is lacking in your relationship to have caused you to make this decision? What brought you to her door? Clearly this isn't for you and you feel you've made a mistake. But that's all it is. A mistake. We're all human and we screw up from time to time. Chalk it down to experience.
Personally I gave up punting (hate that word) last December and I haven't seen any Escorts this year at all. You just take it one day at a time. But its different for me. It's a mild addiction and one needs to recognise that.
For yourself, this is clearly something that's not for you. What you should do is talk it out with a counselor or therapist and not anyone close to you or your girlfriend/partner. Find the deep root of your problem that way.
Take care.