Will It Ever Get Better

New to this site and forum and having a particularly hard day.  My husband was diagnosed with ADHD 15 months ago at age 39 after years of dealing with anxiety and depression and not being correctly diagnosed with the underlying ADHD he's had his whole life.  He is now on medication, going to start working with an ADHD executive skills coach, and we are seeing a couples therapist who specializes in ADHD but the rollercoaster of this ride has felt unbearable at times and is making me question whether or not I can stay in this marriage.  I'm worried so much damage has been done over the past 9 years before his diagnosis that we can't climb out of it.  We have a young son and I am currently pregnant.  I am the over functioner/planner/captain of the family.  If I get sick or need rest, which has happened a lot in this pregnancy, not only does everything seem to fall apart but my husband is also resentful and, quite frankly, rude to me when I'm ill instead of being a caretaker.  It's like he just gets so overwhelmed he can't handle it, shorts out, and I end up having to either A) call him out on it after I wind up being so exhausted I'm in tears or B) I just have to take care of myself when I'm falling apart and don't have any juice left but I do it anyways.  I am the one who has to clean up all the messes, carry the mental load, and be the primary parent while trying to pursue my own career (which has certainly suffered as a result of having to pick up the pieces of messes my husband has made including some major financial indiscretions of his).  I struggle with trusting that things will improve or that he will ever have the skills to be the kind of partner I want.  I can tell he's trying so hard and there are so many things about our lives that are better now that A) he's been diagnosed and B) that he's started medication.  But it just seems like we're in this constant cycle of making headway a few inches but then immediately getting slammed back several feet - it never feels like we're in a place where we can hum along and enjoy our lives for long stretches of time.  It always feels so hard and like if one thing maybe works for a few days something else inevitably goes wrong and it's a dumpster fire; it feels like other couples who don't deal with ADHD have easier lives.  I don't feel like I can ever trust that the changes or good times will last.  How do you know it's worth holding on and how do you know that things will get to a place of being more manageable?  I feel like I'm drowning all the time, not getting what I want out of the marriage, and that I'm constantly being asked to be patient as he learns how to manage this.  But when do I get to feel like things are joyful and enjoyable and that I have an actual partner who feels like a partner instead of another child or a weight constantly dragging me down?  It feels like I've lost the ability to see what I like in my husband or, even when I do, something ends up wiping it out it when he inevitably drops the ball.  He is a good man with a good heart, an excellent father and I can see how there's a world where we could be so happy together.  But when do you know that it's never going to be like that and you're just fooling yourself into staying in a miserable cycle?  I truly don't know anymore.  Am I asking for too much?  Am I expecting too much?  Do I just have a fantasy of being with someone who doesn't really exist and if I stay or if I go I'll just be disappointed either way?