He wanted a threesome with a 16 year old girl and then became aggressive ending up in this type of rape. It shows calculation, determination, aggression and awareness.
This is so true. He SO wasn't triggered. Just look at what you told us, Orion:
(1) He was cheating on his wife
(2) He wanted sex with a 16 year old - a 16 year old who he saw as "weak", as you say yourself Orion
(3) He wanted three-way sex
(4) He was manipulating a 21 year old to help him
(5) He was angered by you exercising your right to say no
(6) He violently assaulted you
It sounds like your mother was not there for you at all. She allowed you to see the psychopath. Even if she didn't know exactly what you were going through, she sure wasn't checking up on you, and I have little doubt that there were signs of abuse to which she turned a blind eye. She let you drop out of school. She let you be rail thin. At 16, she gave you the freedom to spend time with a 25 year old.
I actually
can understand how you don't feel anger at the 25 year old. Your emotional response system was hijacked by the psycho. By the time the 25 year old came around, you were already defeated so you felt "meh, who cares". After all, what's one humiliation compared to living with abuse day in and day out.
The real damage was done by your mother and by the psycho. If you find your rage against them and work through it, then you can decide at that time whether you want to look at the anal rape differently. For now, I think that analyzing the rape is not going to get you anywhere. Even if you are seeing it more clearly now than you were before, you are not in the right frame of mind to work through it. First things first.