I caught my sister's husband in dating app, what should I do?

I saw my sister's husband in Tinder. I was so shocked. It happened few weeks ago and I still don't know what should I do. Should tell my sister?

Background: They have a one-year-old kid. My sister is planning to have a second child. To be honest I don't really like her husband. He is a lazy guy with doing nothing at home. My sister does all the stuff. But my sis loves him so much. Sometimes she complains about her husband but she will still do all the things. You know if they don't have kids, or they are still not yet married, I will definitely tell her.
+1 y
Thanks all the comments. I think I would confront him first and let see how he responses.

Actually I asked some of my very closed friends about this. They asked me not to tell. However, I love my sister, I don't want to hide anything to her. On the other hand, if I tell right away, I don't know whether she could bear the truth. Or maybe, as some comments mentioned, probably he hasn't done anything.
+1 y
I just confronted him, which I got standard answers.
He said he already deleted the apps.
I asked him why he had this apps.
He said his friend showed him this apps and found curious so he downloaded it
After two days he found that this apps is nothing to get so he deleted it.
I think I will tell my sister what I know and what I got from his feedback.
It's her decision to trust or not to trust him.
I caught my sister's husband in dating app, what should I do?
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