Hello there, having a problem here, need your advice

Background: Began MMSL a few days ago. Sex Rank equal. Have been very successful last days by going out a lot, not being around all the time and "accidentally" talking to some attractive women, which she noticed (I am in general good looking and successful, I don't need much game to attract them, though I still want to improve on it). ... You guess it, I got loads of sex after a long time of denial.

Problem: We live together with other people and are for a few days on a trip together. Sex yesterday was denied, I played it cool and she is also on her period.

After lunch today I came back from the toilet, when her head was on the lap of our flatmate, who caressed her hair.

In our social circumstances this behaviour can be socially acceptable, it still triggered my alarm. He was making a lot of jokes, even challenging me with one, when I started to answer, he interrupted. She laughing a lot. He is usually a quite beta guy, small, not attractive (she says so, and he's having a hard time attracting women in general), but with good social skills. They are good friends and hanging out quite often. She admires him in general for being such a feminist and social competent man and for taking care after his child so well (he is kind of single now).

1. How to react properly? I tried to hold frame and left. Should I stay and do something? But what?

2. How to inhibit this behaviour in the future? I guess it would be a bad idea to tell her that it hurts me.

A few minutes later, while I was writing this post, she came to me and told me, she is disapppointed because I left without saying anything. She feels left alone and would like me to accompany her and caress her hair, while she has her head on my lap (She said exactly this). It didn't came to her mind, that I left because she was doing exactly that with another guy. I wasn't mentioning that and told her, that I hear her and will pay more attention.

My guess is that she needs more beta behaviour while she is on her period. Maybe I shouldn't care about that too much, because he seems kind of a beta orbiter. He making jokes though seems quite alpha. I am looking forward to hear your thoughts about this.

(Sorry for my english, as it is not my native language)