I have PTSD, have for a long time. Textbook apparently. Sometimes I am absolutely fine, happy and I cope with the symptoms.
Other times it takes over to the point where it bothers me to a point I think it not something anyone should normally be consistently be suffering. Usually if not always there is a reason, it isn't like other conditions where things seem to inexplicably happen.
I do recognise when it is difficult enough to be able to say "It is bothering me at the moment" or "I'm concerned that this isn't improving and it's too much".
With PTSD it is possible to have this kind of clarity of thinking, the "This feels unpleasant and I am concerned it is going to become a problem" before it is actually a serious problem.
It is then a case of trying to ease things so that it doesn't continue and that is very difficult. It is an exhausting condition because it is always present, it is distressing circumstances that you always end up questioning and therefore not escaping from and reliving that have lead to it and it is permanent work and effort trying to keep in a good way. Sometimes it feels to exhausting and can just be at a loss.
I do think that the mention of suicide and nervous breakdown is serious. Definitely the therapy is important and I hope your DH is benefiting from it and sharing these things. The obvious answer may seem "time off work, change role at work etc" and sometimes that is a good approach, but sometimes the stress as it is in this case is actually more complex because PTSD is very complex, sometimes it's not practical and sometimes it just feels almost worse to choose to be limited in a way not fitting to your natural character and wouldn't be the case if it weren't for the PTSD and the things leading to it. It then becomes a bit circular, because stepping away from something to ease PTSD difficulties actually is a big reminder of PTSD and the trauma, which is not something you want.
It is good that he is sharing with you how he feels and because of that I think it's fine to follow up with him. Ask how he is, ask if therapy helps with these things, tell him you are worried.
As for talking to a doctor yourself, you are absolutely not betraying him and I would have no problem with someone close to me learning more about the condition in a way that doesn't need me to have to try to explain it. Also, you can ask for yourself, how do I cope with a partner with these challenges. What should I be massively concerned by, what should I do in certain situations, what is normal, how can I interpret and understand what is going on. I would not for a second feel betrayed by someone doing this. I would appreciate it.
You also need support. I'm very aware of the people around me being upset because I am, so I try to take on everything myself because I worry for them. That of course doesn't help me, but I don't want them to be harmed. If I knew someone was going to therapy or talking to a doctor about their own health in the circumstances quite honestly I would be thrilled.
I would feel so much less worried about them and the effect on their wellbeing, I would not feel that I had to carry it all myself to protect them because I would know they have support and good understanding, I wouldn't feel as guilty about my experiences causing my family worry and distress, all of that would make me feel much better.
So I would really like for people close to me to have their own support system.
The things he has said definitely merit more attention and understanding for you to work with and not worry about, as well as support and changes so that he no longer feels this way. I'm not sure how the dynamic is on talking about it, but maybe tell him you are really worried and can you please both together talk to a doctor to figure out how can hopefully figure things out.
I think a doctor or therapist for you is a good idea too. It's not betraying someone, it is a massive sign of love to join with someone in this and I know I would really feel better and likely benefit from people close to me being able to do this.