If it is your house, then why is your husband making decisions about who lives in the basement? If it's yours, then tell the guy to leave - in writing! - and if he doesn't take legal action and have him evicted.
This advice may sound harsh, but the whole environment sounds extremely toxic. It's not good for you.
My husband's csa has put a big strain on our lives/relationship and if I was in your place I'd be livid. Plus, if the guys a vet with pstsd, I hope he has no gun around.
[that doesn't mean I do not feel empathy with the veteran, the contrary I'm ever so sad for people who risk their lives in war over nothing but he needs to find help for his ptsd elsewhere, not in the poster's basement. Maybe she can point some organisations out to him or aks him to contact VA]