how to tell a significant other?

I’m 26 and dating with the intention of marriage and kids and all of it. I approached this topic of PMDD with my ex but it didn’t go super well and I do think it was a two way street there. We wanted it badly, but we could never click.

ANYWAY, I met a guy who I really like and I want to be open and honest with him. I struggle with my mental health. I think I always will. We’ve talked about raising kids together and one of my fears is I’ll be more susceptible to postpartum depression(or even mania) and will really need my husband’s full support.

I’m in therapy, taking medication and supplements to help, but I still have bad days. To the point where I emailed my therapist to ask if we could make a crisis plan just in case it gets to a really bad place again and I can’t stop myself from making potentially permanent changes.

How do I tell him that without scaring him off? And when should I tell him? I want to start this potential relationship off with honesty, but not too much out of the gate.