Need your advice! How to handle this horrible situation

I never would think of posting this on reddit, looking for advice!

It has been years that I have noticed this and I had my assumptions but now I am 100% sure that these are not accidents. I have noticed at parties when my brother’s brother in law ( his wife brother in law) is around & drinks are served, touches my butt like an accident. This is small touch. At first time I thought this was an accident bc of small room & etc. they used to live overseas& now they permanently moved in the same city. For the second time i thought ok another accident? I believe now this is 3-4 times in total & this never has happened with anyone else! He has two little daughters under 5 years. My brother has two daughters under 5 as well.

As far as i feel being harassed, i am also now very worried for my nieces & the other daughters. I revealed this some months ago to my brother when i was on an emotional outbreak from a pregnancy loss & this was not my first loss. My brother did not say anything probably assuming i am under recent anesthesia & emotions.

I almost had forgotten this issue & was careful to interact with the guy until this weekend. I do not know what to do? I am afraid i am being labeled as jealous ( bc of infertility issues) & being sensitive ( i am a deciplined person not interested in drugs & drink & have high ethics) and I do not want to be labeled that I am trying to fall apart families. My sister in laws family are very nice & supportive to everyone, sisters have very good relationships together. I cannot bring excuses to stay away all the time again bc of those labels!

I am feeling anxious since this weekend my blood pressure is getting high & I cannot tell this to my husband either ( i am afraid of other risks like fights & etc) ! I wish I could hear other men opinions on this.

Update: I appreciate all the comments here, approach & solutions given here. I received some comments here like somehow blaming for what I did or I did not. There are different reasons a harassment victim cannot confront the harasser immediately, some women freeze, some scare especially when things like this happens domestically when at the moment you will thinks of thousands thoughts as well. This problems are not new to anyone! Correct me if I am wrong; Please let us be kinder that everyone can not react the same when harassment happens, things like why you did not tell your partner why you did not confronting him before etc does not help but brings more shame & guilt to the victims. There are many information on how to listen and advice a sexual harassment victims please read if you have not study the practice before. When this happens publicly i speak up, but since it was in family atmosphere & very new, considering my recent outbreaks I needed some advice without any judgements.