lookingforzen

I'm not sure where to start, I haven't ever participated in this type of forum before...but desperately need some support and advice.
I've been with my husband for over 20 years, and am now in my early 40s. We have 2 teenage daughters. I've always been the glass is half full, action oriented person in our family, my husband typically is the opposite. For most of our marriage I pushed for "happiness" for us...rather than just getting through the days, which is often how it felt. We've had a good life but he never really seemed to get that. A little over 2 years ago, when I was ready to end the marriage if we didn't seek counselling because he had become so negative, he was diagnosed with severe depression, with apparently a long history of chronic depression. It took me by surpise but shouldn't have - the signs were there, and there is a family history, including suicide by one of his parents when he was young. He continued with counselling, and we attended together as well...and he would commit to doing the work to improve (reading, exercise, communication, etc), but never followed through. He got past the severe part of the depression with the help of anti-depressants, but never really seemed willing or able to strive for happiness. In the midst of this I was diagnosed with stage 3 cancer...it was the 2nd diagnosis for me, although the first one was early stage a few years before. The next 9 months or so was spent just dealing with the surgeries, chemo, etc... He stopped his own treatment, saying we needed to focus on me. The reality was, though, that for the first time in my life I wasn't able to be the strong one, and when I needed him the most, he wasn't able to be there as an emotional support for me. That has been very difficult for me. I asked that we go back to the counsellor when my health was stabilizing...and both the counsellor and I spoke to him about how much more was possible, with some work on his part. The counsellor understood where I was at, and suggested I give things a year before making any life changing decisions, such as divorce. We tried to let my husband know that if things didn't improve I was likely going to leave. That was a little over 15 months ago.
After a few attempts at trying to communicate with him that I was extremely unhapy, and him committing to think about things and "get back to me", then never bothering to bring the subject up again - I decided I was "done". I let him know I no longer considered us married, and wasn't going to ask or expect anything more from him, but that I wanted to remain together to provide some stability for our kids - likely till our youngest finished high school. In many ways I know this may be cowardice on my part...in some ways it's easier to maintain status quo...in my nice home, not having to share our kids on important holidays, etc...but the other truth is our family has gone through hell the past few years, and while my kids don't know about his depression, the atmosphere has changed in our home...and providing stability is very important to me, especially having come from a divorced family that still has trouble being in the same room together!
Other than to say he isn't happy with how things are and he hopes they get better, he's done nothing. And now I feel like I'm drowning in sorrow, and ironically, am in my own form of depression. The last few weeks of family get togethers, and pretending things are normal has been brutal. I need to take care of myself - I know that - and part of that is likely ending this marriage now rather than later. But I can't help but worry about his mental health, and the impact on our kids. What if he loses it - with drinking, suicidal thoughts, or worse? How do I then look my children in the eyes (never mind myself in the mirror), if I could have prevented it by just staying? And how will my children feel about me, knowing that I am the initiator of the family break up?
Any advice out there?