Your post brings up a number of issues, I think. The first is that it's not strange at all for a guy your age to want sex really bad; it's normal for a teenager to be thinking about sex all the time. For a guy who has been abused these feelings can be intensified by the fact that he is in fact sexually experienced, even if, as you say, not by his own consent. This can be very confusing: sometimes a guy feels that in some ways he doesn't want sex and isn't ready, but also feels that "my body won't listen to me". This is something to talk about with people you trust, like your grandfather and your T.
If you freaked when you had in mind to have sex with your bf for the first time, that doesn't make you a basket case at all. It just means that you weren't ready. Talk to your bf and try to let him know that approaching the idea of having full sex is something that's going to take you some time. Let yourself ease up to the idea at a pace that works for you - you don't have anything to prove and you don't have to be in a hurry. That is, don't think to yourself, "Will I be able to have sex tonight?" Let things happen as you feel comfortable with them. If you can be more relaxed and at ease, that will make it easier to take the big step when it feels right for you.
I can just imagine how embarrassing it was to lose control of yourself, but hey, this happened because you panicked. Don't blame yourself or beat yourself up for this. Again, what you have here is another issue to talk about with your T. Please don't hesitate to do that. Therapists have seen it all, Jason. A bladder problem is of course a disaster for you, but for the T it's something he has seen many times in the past. The T will in fact admire your courage for being able to talk about this.
Nobody living can ever stop me
As I go walking my freedom highway.
Nobody living can make me turn back:
This land was made for you and me. (Woody Guthrie)