Tenant moved out - Discovered something in his lease

[Tony Kim]

OK, this might be a total jerk thing to do, so I thought I'd run it by you guys first. 

I have a Section 8 tenant who has pretty much been the ideal tenant who keeps his place very clean and always pays his rent on time and is a very friendly, outgoing guy. 

Several months ago he got married and his new wife and new step-kid move into the unit, but he does not tell me about it. I only find out about it a little later because the tenant calls me to let me know that the rent will be a few days late because his wife got a restraining order on him for hitting her. He spent the night in jail and his brother bailed him out, but he can't go home because his wife is living there. This is of course, all a big surprise to me. Eventually, it all works out because his wife decides not to press charges and they go to marriage counseling and they are doing much better now.

Several months have passed now and his voucher request for a 2 bedroom has just been approved and so he gives notice to me and his final day was yesterday. So now I'm going through his lease and discover that for any additional occupant that moves in, he is required to pay an additional 10% of rent. In other words, he's technically should have been paying me an additional $372 per month for the past several months.

Am I allowed to deduct this amount from his security deposit? If so, would you guys deduct it? The way he's been talking, I can tell that he's really counting on the security deposit money. Thanks in advance for your input!