May be a bit harsh here but we expect family to behave in a positive way. Unfortunately, those expectations can be different to the norm.

There will be many differing views of your male cousin's behaviour, even condoning it due to inexperience or embarrassment. Likewise, they may not understand your issues. You have the right to set boundaries and if you feel uncomfortable, the right thing to do is leave.

I'm pleased your aunt has reached out to you. Also that your mother is supportive. I'm not a fan of social media as it's often use to "air dirty laundry in public", causing destructive rather than positive experiences.

By leaving you not only setting boundaries but also personal standards. A good example to your younger cousins too. It's good that some family members recognise this but we should never be forced to attend family events just because it's family