Would you tell someone??

My ex boyfriend (my baby’s dad) and I broke up a few months ago. Since then, I made a tinder account, just to see what the fuss was about. While swiping through, I found his sisters husband on there... all his profile says “just looking for fun”... that sister & I aren’t close, so I don’t know if/how I should approach that situation. I do know that they just had their 3rd baby together about a week ago, though.