34F seeking advice on relative behaviour.

I am 34F living with my husband and kids in Delhi. Not native of Delhi but settled here and working. Have used Reddit in past but then got off. Now again here as i seek some advice.

I have a distant relative who wanted to get their son into Civil services preparation and they contacted my mother if i can let their son live with us, since they are not so well to do and can't afford rent. We live in a 3bhk flat here, so we discussed an agreed on he coming here and joining a class with his graduation.

He is 19 and we barely spoke 2-3 times occassionally whenever we met in family gatherings. He came and started staying with us. All was normal until i noticed he has kept one of my undergarments that i have been looking for a while and went missing in home. I found it while cleaning his room when he was away. I understood a few bits but still wanted to check more. Started noticing him more and i found he finds his way to my clothes whenever he gets a chance to sneak in and touch them.

I haven't confronted him on this till now and neither have told anyone. If my husband comes to know he will get him out and i dont know how will his mother react. Is it worth confronting or i should let it go casually?