I doubt the therapist will think you're a horrible person. It's not like you raped your friend. I'm not trying to minimize what you did, as I think it is morally correct to recognize it wasn't an ok thing to do. I don't particularly agree with the idea that it is acceptable to learn how to act as a young adult by doing stuff like this. To me, that reflects more of a "boys will be boys" attitude. I would prefer that people be taught from a young age that this sort of thing isn't ok, rather than learning by trial and error. But I would suggest that society is partially responsible for this transgression and your ignorance that it wasn't ok, and that what is required of you is to recognize the error and learn from it - which you have. Unfortunately, it is likely that this wasn't the last time your friend endured unwanted physical advances. I doubt that what you did stands out in her mind to a degree that your immense guilt is warranted.

Try not to beat yourself up. We can't change the past or the things we have done. We can only take responsibility for our past actions. Remorse is appropriate, but wallowing in self hate is not proportional or productive. Hating yourself changes nothing and serves no one. I would be very surprised if your friend wanted you to be this hard on yourself.