It's sad that you feel like you don't have the luxury of "breaking" down. I think it would be good for you and your long term health to change your mindset on whether mental illness is a failing.
I mean it might help not to see mental stress/illness as a personal failure- you seeing your daughter's anxiety as parental failure, or your husband's illness as weakness. Bottling things up is probably a recipe for future trouble in that respect.
Can you seek counselling via your GP, given the situation with your daughter's and husband's health? Or are there any support groups for relatives of people with your husband's condition?
I used to get really annoyed and frustrated that DH didn't just know what I wanted. I assumed I just knew what he wanted because I had had more relationships than him.
Once we started talking about it, lo and behold, it turned out I didn't just know what he wanted. Because funnily enough he wasn't just a carbon copy or composite of everyone else I'd ever been out with, he was his own individual person. That was an eye opener for me.
Think about it this way- who's better at relationships? Someone who has a lot of relationships that end or someone who gets married to the only partner they ever have? The likley answer is that both people have some strengths and some weaknesses and they can learn from one another.
I also started realising that having to a do a bit of talking, teaching and learning was part of the ticket price to a relationship with someone who was unlikely to be unfaithful. Swings and roundabouts kind of thing.
And wanting a partner who is highly likely to be faithful isn't necessarily just about wanting security, rather than that person. It can be about wanting the kind of person who is loyal, faithful, secure, who takes commitment seriously. The things are linked.
It's easy to come up with a checklist of personality traits for the ideal person in your head, but really, does that person exist? Some personality traits are more likely to go with others. So prioritising what you want long-term doesn't mean settling, it just means prioritising what is important to you and realising what type of person is likely to be able to provide that. So decide what you really want out of a relationship and take it from there.
It looks like you are very stressed about a lot of things, and you need to deal with those things one at a time, rather than looking to make one sweeping change that will solve everything. I think you do also owe it to both yourself and your husband to give it a decent, concerted attempt to fix it. Then if you do move on, you don't look back with a load of "what ifs" later.
By decent attempt I do think you need either counseling/marriage guidance or a programme you can follow. There needs to be some outside influence. Behaviour change takes time and repetition, so it take patience no understanding and an appreciation thatYou both need to be bought into it.
I thought it would be difficult to get my dh to buy into it, but I sat down with him, told him how unhappy I was, told him the reason I had bought a new suitcase was I was thinking of leaving. We'd had so many rows in the run up to that, he understood that I was very unhappy.