Husband’s best friend’s sister. How to address

So this is about my husband’s best friend from college his sister.

Backstory husband and I have been together for awhile since we were teens in high school, dated throughout college and married after college we have a 1 year old now.

We’ve had our fair share of issues. Anyways so during a time we were on a break in college, I was out of town, he took his best friend’s sister to a military ball. Obviously I was hurt whatever we made up got back together. This was years years ago.

Fast forward to last year. She contacted my husband, who is in the military, telling him about her husband who is also military and how to get a divorce, they have a baby as well, I thought it was weird because 1. We don’t live in the same state. 2. Why would she call my husband of all people she has family in the military herself.

So my husband like hears her out talks to her blah blah. I don’t make it a big deal trying to get let it get to me.

Well I’ve noticed he does Snapchat her and social media she will like pictures he posts NEVER ones with me in it. And she commented recently on a picture of him and our son.

Like I get we have kids the same age so I see that as a connection? Maybe. But idk something’s not sitting well. He knows how I feel about social media anyways and where boundaries goes we’ve had issues with that before.

What do y’all think