At what point do you stop fighting for your marriage?

I was trying to explain this to a friend.  My husband has decided he wants to leave, and since i've been pretty miserable with him lately, I didn't oppose to the idea.  But still I still have thoughts about getting back together with him, still trying to mend things, still trying to work it out.  My friend thinks I'm nuts.  Ok, nuts isn't the right word, but he couldn't understand why I would want to go back when I've been so miserable.

What I tried to explain to my friend is that my husband is an amazing, wonderful person.  It's this out of control ADHD that's screwing things up.  It's not 100% the reason, but I believe it's certainly a big factor.  Looking at the overall "big picture", we are great for each other.  Our friends who know us, despite knowing our struggles, still think we're the perfect couple.  Friends envy the relationship we have.  I can give you a hundred reasons why we're made for each other.

But unfortunately my husband loses sight of that as he's currently hyperfocused on what's wrong with our relationship.  This is not the first time he wanted to leave.  Each and every time, I have been the one that fought for our marriage.  I'm the one that has agreed to many changes (I know I'm not perfect, I'm willing to work on my own issues), I'm the one that ends up going through hell trying to convince him to stay.  And when he does decide to stay, it's because he usually realized that he was being petty and stupid to want to throw this marriage away over a little whim.  So he does see what I see when he can see clearly.

I feel like if I can get my husband to see clearly, he will understand what I'm talking about.  He's mentioned it before many times, we've got a very strong relationship.  He knows we complement each other well.  Until he starts hyperfocusing on the problem, then all of a sudden the relationship's not working out.  He's currently unmedicated.  He was on adderall for a while which he liked a lot until the effectiveness went away when his body adjusted to the medicine.  Then he just quit and has never gone back.  I want to convince him to try taking adderall again before making the decision.

But at what point do I stop fighting for the relationship?  I'm getting tired.  There's a part of me that wants to let it go and move on because I don't deserve to go through this crap.  And there's no telling when he's going to hyperfocus on something wrong in our relationship again and want to leave.

There's the other part of me that refuses to let a good relationship go over a trivial issue that husband is hyperfocused on and can't see past.

An older friend of mine told me, society today, people give up too easily and for the stupidest reasons.  She said that's why there's such a high divorce rate.  At the first sign of trouble, it's divorce.  Back in her day, people worked through their troubles.  People made compromises, and learned to live with the little annoyances and enjoy the bigger reasons why fell in love in the first place.  No one is perfect.  What you do is you find out what's really important in a person, and learn to deal with the unimportant things.  I feel like she's dead on.

Do I keep fighting for this or do I need to give up hope at this point?