Speaking from both personal and professional experience, I wouldn't recommend dating someone you met in treatment.

At the hospital where I work we advise all patients to avoid building relationships, including friendships, with people that they meet in treatment. It still happens, because people can feel very close to others that they meet in treatment because they often have a lot in common and share a lot of personal stuff in group therapy, which is actually problematic because then confidential thoughts shared in that setting leave the safe space of treatment.

A number of our patients do wind up dating, which we find out about because they either continue treatment in our outpatient programs or come back to inpatient, and those relationships almost always end up a source of stress for them, rather than a positive support. And sometimes it can get very, very bad.

I don't think it's bad to date someone else with mental illness, in fact, it can be really good because you understand each other in ways many people can't, but it helps if at least one of you is in a decently stable place, as opposed to someone else who is currently in acute treatment. I have been in relationships with a few other people with mental health issues, and while some, including my current one, have been great because we started things in a good place, I've also had one where we were both in an acute state and it was traumatic enough to mess me up for years.

Just saying, be careful, and try to use your best self awareness going forward.