<human>: This is my first reddit post so be kind. 

My [F26] boyfriend [m29] of 8 months sister-in-law [f34] is completely monopolizing his time and manipulating him and being really mean to me, but he doesn't see it. It's like she has marked her territory and she doesn't like the new girlfriend, me, moving in, and it's very frustrating. She purposely leaves me out, openly flirts with him, etc. 

His relationship with her is very strange. He considers her a great friend, even though I've brought to his attention the way she treats me. He will spend all day with his brother, and still wait for her to get home from work to say hi. Even though I am home alone cooking him dinner. It seems to me like he chooses her over me. I don't know what to do!

Her mom even refers to him as "her son in law by default". She also brings him presents whenever she is around. It makes me very uncomfortable. I'm sorry, but that's weird. The sister in law loves it. She seems to want her husband (his brother) and him at her beckon call. When we are over at his brothers house, she orders him around and he will drop whatever he is doing to please her. She knows exactly what she's doing! The fact that he doesn't see it, drives me crazy!

He says he doesn't see the strangeness of their relationship. How do I make him see it?

Give me the gist of the text in a nutshell
<bot>: my boyfriend's sister in law is tormenting our relationship. Their relationship is very strange and I don't know how to make him see it.