OP I am so sorry you have had to witness this breakdown, and go through this yourself.
I will be honest, I know very little about bipolar, and also everyone is different, but thought I might be able to add something to the conversation.
I am currently in hospital on a section 3 after relapsing with my schizophrenia due to not taking medication. It is actually my fourth psych admission this year, all due to meds.
I was apparently very unwell when admitted, in quite a similar way to your BF. I hope this isn't TMI (please report my post if it is), but I thought Satan was trying to rape me to impregnate me with his child who was going to destroy the world and then I would rule hell with Satan. So I put razor blades and a hypodermic needle in my vagina, and safety pinned my labia together to stop him. I also had auditory, visual, and somatic hallucinations of Satan and demons. Stopped eating for a couple of weeks, and tried to stop drinking too, so that he wouldn't hurt my DN. Anyways, so I was quite out of it, although I did recognise people etc. I have had these same experiences before/during each hospitalisation this year (and previously). Each time they say I don't have capacity and then section me, operate on me when I beg them not to, and give me fluids.
BUT I am really high functioning and get better really quickly (I am fine now and going on leave tomorrow). I just need medication and then I am perfectly well. I am top of my class at university (maths degree), have friends and live alone.
When I am off meds I am a different person, and pretty scary to be around apparently. Do you know what made your BF relapse? If it is medication then there are things they can do to make him stay on it. I am normally on a depot (where you get your medication injected fortnightly/monthly) so they don't have to rely on my taking oral, and am also going to be back on a CTO (community treatment order - like a community section) so that they can readmit me and forcibly inject me if I refuse my depot in the community. This could be an option for your BF if he is refusing to take meds reliably (or forgets even). A lot of the depots that work for schiz also work for bipolar.
Also, you are not responsible for giving him care. You have to put your children and yourself first, especially at these early stages of the relationship. I personally am very independent and feel really embarrassed at my family and friends being involved in my treatment (think police looking for me, doctors phoning to tell them I'm having surgery, and what for etc.). I am quite mortified and would rather they knew nothing about it. He may well be the same. He might be really embarrassed when he comes round.
My family are used to it after 20 years of me being ill, but still find it very distressing, so it must be really hard for you, so you need to get help. The ward should be able to give you carers info, and some places have carers support groups.
So to answer your questions more succinctly: yes, I imagine he will be back to his usual self before too long, especially if this has happened before and he has been fine again before (although I appreciate what others have said that you may have known him in a manic phase only - as I say, I have no experience of bipolar). He may well be very well managed on medication, as long as someone can ensure that he takes it reliably, in whatever form that takes. And he shouldn't need too much care and if he does, then that should come from mental health services (although they are notoriously bad). If he is sectioned I think they have to put him on a 117 which means they have to provide aftercare (although not actually sure that applies with a section 2 - but he'll probably be put on a 3 soon).
I hope you are okay. If this is too much for you then I would consider leaving him. It sounds awful but I know I would hate someone just putting up with me because they felt it was wrong to leave me because I was ill. Not saying that's what you are doing. I understand you love him, but it all sounds very intense. If this relationship is damaging you, then you need to take a step back. Maybe reassess the situation once he has been stable for a year or whatever.
Hope that helps 