They will need to treat him for awhile/depend on the doctors notes to stay in. This is gonna sound bad so please take it as a generalization and not an attack on you or your husband- The army is facing so much in regards to the suicide rate, they would rather take someone who attempted suicide-get them to stable status and put them out in the hopes of removing the stressors leading to their attempt, then the va takes care of them and it becomes a VA stat not an army suicide stat.
IF your husband is really good to go and is being railroaded, I highly recommend seeking second opinions from civilian providers and getting those notes into his mental health record. and fighting all the way through tot he formal board/surgeon general of the army.
To be blatantly honest however, if your husband is an MP and that is one of the few jobs he qualifies for and is known to be "suicidal" in stressful situations then the armed forces may not be for him. If he did not try to OD, he said he did which meant he was using an escape mechanism, if he was manning a gate in the stan and shit got rough would he do the same thing leaving the gate undermanned or forcing someone else to pick up his slack? it sounds bad and I am sorry, I have put a lot of people in the service as a recruiter and the ones that did not qualify for the AF i helped put in their second or third choice, one constant no matter how good my sale was, no matter how hyped up I got them on going in etc. NOT EVERYONE IS CUT OUT FOR OUR LIFESTYLE and its best to find out early vs after 3-4 years etc.