anal sex..advice please

little back ground. I've been raped in the ass while drunk and just a few months ago an ex shoved it in and ripped me w/o consent. I've never done it willingly aside from the tip then get scared and change my mind. my current bf really wants me to let him..I'm terrified but want to do it for him. Question is, how do I get out of my head? How can I make it pleasurable for the both of us? I'm pretty ignorant to it. I tried it tonight but didn't do much or for long..he wants to do it next time and i want to be prepared! any advice or tips are appreciated