PLEASE HELP! My Sister Wants To Quit Her Young Marriage

Good day fellow readers, I hope your day is going well, though mine didn’t start so well. 

I am a guy from a humble background. My parents had only two children, myself and my younger sister, who is now married with two kids.

She had her last baby boy some time early this month. Her marriage with this guy (my brother-in-law) has been one I considered relatively peaceful.

That is from my own perspective, knowing that there’s no marriage without one or two misunderstanding here or there at some point.

Well, she found out that her husband got another girl pregnant, who gave birth to a baby girl. My sister found out after she gave birth to her first son.

Her husband was the one that confessed to her that he has another child outside their marriage. They settled the issue and moved on he promised he would end the relationship he had with the baby mama.

Last year, during the COVID-19 period, my sister found out that he was still seeing his baby mama after she saw their chats.

She confronted him and he denied having anything to do with the baby mama except for sending money for his daughter’s upkeep once in a while.

It was a big issue which was brought to the attention the two families. They found a way to settle after a lot of pleading and talking to the two of them.

To cut the long story short, she sent me screenshots that proves that he is still seeing the baby mama.

In one of the screenshots, he wants to see her in their normal place and the girl agreed but doesn’t want them to have sex on this particular occasion.

My sister has bad temperament and it is not easy to calm her down when triggered.

She’s threatening to quit the marriage, and I fear she may do something wrong this time around.

She is yet to confront her husband because I managed to convince her to keep it on hold till she calms down.

Note : My Dad is late and my younger sister is a housewife hence solely dependent on her husband.

Please ignore my grammatical errors. I am putting this out here because I have ran out of ideas.

What Should I Do?