He is absolutely not in the right head space to even think about getting into a relationship and the fact he is suggesting a date is a massive red flag.
He should be focusing solely on himself.
I have had family members and friends who’ve been sectioned and they are all lovely people, so I would never say not to date anyone who’s been sectioned but no way would I ever say to date whilst they have been sectioned.
In fact, I would never date anyone who is currently sectioned in a MH facility, prison, living with an ex wife or their parents (unless there was a good reason), as way too many people cannot be alone and they will try and cling to people so that they can live with them/be taken care of.
You also need to think about how fragile he is and what happens if you’re not ready to commit to anything too serious but he wants to move faster or you want to end things completely - he could end up hurting himself and you’ll struggle to end things as you will feel guilty as you have him hope or whatever.
Unfortunately people can be trauma bonded and form attachments with people because of past trauma and it’s hard to see whether the person is actually right for them.
You are going to do what you want to do but my advice is to take things very, very slowly and remain just friends for a long time.
Any kind of pushing from him to make things go faster or if he’s starting to struggle with his MH again, then run!
I am assuming you don’t have kids?
Who do you live with?