My life is falling apart

I’ve been with my partner for 2.5yrs, been living together for almost 2yrs. He (now 40) stepped in as a step father for my 3 kids and was an amazing step dad to them, taught them things, took them places, loved them and cared for them without a question of doubt. Don’t get me wrong, my kids are hard. 2 neurodiverse - a of which is 10 this year and I even struggle with her to the point I have considered giving up my parental rights to her.. but obviously I could never! We fought, nothing ever serious. But I stayed a few times I shouldn’t have, like when I found out he was an alcoholic and was drinking behind my back - and then again when he was doing it again and came home one night after ‘going to get icecream’ and he was plastered within half hour of being home.. anyway, I forgave him and he started medication to stop drinking. Things got pretty bad between us about 3 months ago but we promised to try and continued to choose one another. That was until 8 weeks ago when he told me he was going to leave and go stay somewhere for a week or so and sort his head out, that didn’t happen.. but then 7 weeks ago he left for his mums house one Friday night with a bag and said he’d be back on Sunday. When he got home on Sunday, it was a straight up ‘I need a break, I’m here to get some things and I’m going. I don’t think I can be a step dad, I’m not a good role model’ We’ve been talking and seeing each other on weekends, up and down more times than a roller coaster, I’ve never seen this man cry until this past 7 weeks, he’s in a really dark place. I’ve watched my son (8) and youngest daughter (6) cry and be heartbroken that he’s gone.
It’s now gotten to the point where I’ve decided I’m leaving him be - I’m not letting go, but leaving him to be in hopes he’ll do the right thing and seek the help he desperately needs and has promised his mum and I he’ll get. I can’t let go as I have never felt a love like this, not even for my ex husband/kids dad and he has also said he never loved his ex of 8yrs like this. But my whole world is crashing and burning, he was my safe person, my brain was quiet when I hugged him, my face lit up everyday and instantly the world felt lighter when I heard his car pull in the driveway, any problem or good thing that happened - I went to him. Now I feel homesick, I feel so empty and lost. Again - never experienced this feeling after I left my ex husband.. I didn’t think I’d be heartbroken at 33 years of age, I didn’t think I’d be witness my kids be heartbroken either, I didn’t think this would be happening, we had spoken about marriage, he had even told me how he planned to propose when the time came.. I just don’t know how to continue life without him by my side, without messaging him to see how his day was or to fill him in on mine, how to deal with life struggles without him..