To set up boundaries with friend because of her partner?

[Jaggedpill]

Right, please keep me honest if I am being unreasonable because I might be.
My best friend confided something in me a few weeks ago, and I cannot let it go. Basically her boyfriend assaulted her (she did not use these words, but this is the nicest term I will describe it as), and she decided to forgive him and move on.
I know that I should accept this, but the more I think about it the angrier I get.

I know that I cannot change her mind - if she has forgiven him then I need to accept it, but why did she tell me then?
Secondly, I do not want him anywhere near me, and this is bound to cause some issues if she wants to bring him along to events. For now I have decided that I just will not be OK having him in my house and near my family, but I have not told her so because I am afraid of embarrassing her. I obviously cannot object to meet him in other circumstances.
I don't want to alienate my friend, but I am also not sure how to deal with this knowledge.
Is it reasonable to set up boundaries, even though it does not affect me personally? I feel somewhat selfish, and that's not who I want to be. I am worried about her but I am not sure if she is ready to deal with this yet.

This is what I would also do. Last thing you want to do is alienate her and make her feel like she has no one.

My friend is in a same sex relationship and his partner is abusing him psychologically. I have made it clear that I don’t want to be around him. I stop short of saying don’t talk about him, as I want him to confide in me if anything is wrong but I don’t want to see pictures of days out etc. And I won’t mince my words if he asks me what I think.

Thanks all. I cannot ignore this, but I am "ok" to pretend that everything is alright for the time being so she won't feel isolated. I just hate this whole situation so much.