Many years ago my dad met his partner in what was called a “halfway house” back then. She had previously been sectioned.
They were together 15 years, bought a house and had a mortgage. He loved her very very much. She went missing three times. The first time she turned up in Israel. The second time she turned up in a psychiatric hospital on the south coast. The last time she went missing for good and when my dad died, we still hadn’t found her.
She came into my life when I was about 10. I really loved her. She was funny, kind, intelligent, full of empathy. She wasn’t maternal but she was wonderful to me and my DB.
People who have been sectioned deserve to be loved too. They deserve to find someone who accepts them for who they are. And that means accepting and understanding that there may be relapses and that their MH may impact the relationship.
OP, you came to this thread to ask for opinion on starting a relationship with someone who is currently sectioned. And you have a child. I appreciate that you have since decided to remain just friends for now, but I think the fact that you’d even consider this is quite concerning. You might want to consider why you thought it might be feasible - do you need counselling yourself? A man who is currently sectioned is in no way fit to embark on a new relationship, no matter how kind and lovely he is. He is in an extremely vulnerable position and starting a relationship with him isn’t even a question. The concern here is not the conclusion you’ve reached but how that wasn’t obvious from the start - even more so as you are a parent.
Also you’ve mentioned that you both have the same trauma. I’m not sure this is a healthy basis for a relationship either.
By all means continue your friendship. If he returns to the community successfully, is stable, and healthy mentally you can both reconsider things at that point.