TW: drugs, incest, older sister/younger brother,

Hi guys, this is my first time posting here so I hope I'm doing this right! I'm sorry if this is a little hard to follow and a bit long-winded, I'm not much of an author but I'd really appreciate it if any advice could be given. smile

I am 20 and my boyfriend is 22, we have been together for almost 2 1/2 years now. I always had my suspicions that he had suffered some kind of abuse/trauma as he has some anger issues, was using hard drugs from the age of 13 (meth, pills, weed etc) until I met him, has a very low opinion of women, had never had a relationship other than casual sex before me, has an unusually high tolerance of pain, usually hated being touched.
His family seemed very nice (very middle class, two parent home.. pretty much the perfect atomic family) and had always given the impression he was a good little boy until the age of 11 or 12 when he started to become very angry and hard to manage seemingly overnight, which further caused me to assume he has suffered in some way.

After some gentle encouragement my partner (we'll call him BB) explained to me that he was sexually abused by his older sister for sometime around the ages of 10 to 11. His sister (SS) is 3 years older than him, making SS around 13-14 when the abuse began.

BB explained to me that SS would occasionally come into BB's room a night and would molest him. BB never went into any details other then that he had told SS to stop more than once and that they never had intercourse.
From what little BB has said this happened more than 5 or 6 times.
I am the only person he has ever told.
As another odd side note, BB lost his virginity at age 13 or 14 to one of SS's friends when she was having a sleep over one night. BB says this was consensual but does get very tense whenever the issue is raised and has mentioned how odd he thinks it is that a 16/17 year old girl would want to sleep with such a young boy (BB was always a skinny, lanky late bloomer too, which I think makes it more odd). I assume that SS would have known what her friend was doing with BB, as teenage girls cant keep secrets and love to gossip, making me more suspicious.

BB's sister is now 25 and lives a few suburbs away. We see SS every few weeks when BB's family has dinner and they occasionally talk on the phone. They have a 'good' relationship. The topic has never been brought up by either of them. BB says he doesn't want to confront his sister as it will hurt his parents and destroy the family, and that he has mostly forgiven his sister.
I know I should take him at his word, but he has admitted he doesn't like to think about it a it makes him angry and uncomfortable, and he would like to know why she did it and if she perhaps had been abused.

I struggle very much with begin around his sister now as I can't stand the thought of the pain she has caused him. To me the biggest point is her age at the beginning of the abuse.
13 is definitely old enough to know her actions were wrong.
SS has also worked in the mental health system since leaving high school and has much knowledge and experience with trauma and abuse victims. It bothers me so much that SS could see her brother becoming a meth addicted alcoholic at the age of 14 and did nothing to suggest him help with all the resources she had available. I know that through her studies, SS would have been aware her abuse caused BB's anguish resulting in addiction.
Also, his parents hold much blame and guilt as they think something in their parenting went wrong to cause his problems.

Sorry to digress there, but I guess I just want to know:
- Should I encourage BB to seek professional help as this is obviously still effecting him?
- If he won't seek help, how should I support him?
- If anyone else has experienced being molested by their older sister, what can/should I do? I can't find much reading material about this particular kind of abuse.
- Should he confront his sister, if so, how?
- Has anyone confronted their older sibling abuser before?

And I feel very selfish asking this, but how should I act around his sister? How can I get my anger for her in check?! She makes my blood boil.

Sorry this was too long, I hope you understand. Thank you for taking the time to read and reply! smile