My sister's husband in Thoughts on thoughts

Why do men act the way they do… this would be my sister’s second marriage. The second time she has met a man and within a month is engaged and married. She doesn’t get to know them first or see how they are. Yet she falls in love and now she has another last name.
The first was a month and then engaged but had to move to another country due to miliary.... we also moved to the same country because of course we are also military, my dad I mean, so we followed… she finally after a month or so found him and they go married. That one lasted about 10 years and two beautiful kids who are now in their late and mid teens. She meets this new one and they basically elope, after a month and don’t tell anyone what was going on. I found out on accident. She then has her third baby who is also amazing and is now 10. this marriage looked like it was gonna be okay… he’s currently texting or, sexting three different woman he met on his video game. They know he’s married, and my sister knows about this situation… they are going to try marriage counselling and I wish them luck, and her happiness....