When you masturbate, is your mind super engaged and aroused? Or is hard to get or stay really mentally turned on? And when you say you don't feel anything until the end, are you literally not feeling any sensation? Or is it more that what sensations you are feeling are pretty dang underwhelming?
I'm glad to hear you're working with a therapist. Since there's sexual assault in your past, is that something you've been able to talk with your therapist about and get support around?
I do want to note that, if you're looking into anti-depressants, some of the commonly prescribed ones can have sexual side effects, including making it harder to get aroused or to orgasm. That's not to say you shouldn't get on them if they're beneficial to you, and there are ways of dealing with those side effects if they arise, but I wanted to let you know that's a possibility.