Hi there!
Welcome to the family. I first want to say I am sorry that you and your partner are having such a hard time. It sounds very painful and confusing and you feel like he has gone too far. It is extremely hard to understand our partner's behaviors. I have found that a huge dose of compassion makes a big difference. Okay, so I wouldn't do or say things he does at times, okay, but can I relate to the feeling? Can I even identify the feeling? When I can than things make more sense and I can judge less and do more to be helpful.
I was also walking around in the past thinking I could communicate well and he could not so therefore = all his fault and I just tossed it in his lap to solve some days. But you know what? My communication skills were rusty and I needed a total reboot on them. This site is amazing because it has free/easy/fast stuff you can use/practice today that will keep things on your side of the relationship at a better level. So, "are you [we] partly to blame?" Well, yeah, we are part of the communication and while it is understandable we are frustrated and confused, once we know what's up, we have to improve ourselves and give our best. We can't just be mad at them, fold our arms, withdraw, and make them fix the relationship on their own for us. I tried and that didn't work!

My suggestion is to work on your own communication mistakes - that is the fastest thing and what you have control over in life. Take that seriously. It could deescalate things just enough that you can get to other issues on the plate here.
With a compassionate heart we can see he too is having relationship problems and is very confused and he has no tools to deal with that in a healthy way. That is a hard place to be in. He wanted someone to talk to, that is a boundary you didn't want him to cross, but that is not necessarily automatically "bad" (in my book, but I've stayed friends with ex's.) If the ex is a friend, and only a friend, and did provide him some understanding I would not fixate on it too much at the moment. He's about putting himself into a hospital so he must feel at the end of his rope that takes the priority here in my estimation. He needs people to care and relate to his feelings. My husband was actually telling me for this for years, that I didn't care about his feelings. I did, but I was not really addressing it because it was so BIG and confusing. I could not relate to his level of intensity and I have to admit I didn't do a very good job of responding to it. Now that I understand his level of feelings, and don't judge them, just work with what is, we do much better.
Hopefully others will chime in on other issues you've raised here.
Keep posting and asking for specific things we can collectively point you to to help things improve!

People here have a lot of insight and wisdom that is worth engaging with.
Wishing you well!