Scheduling Challenges

I've been dating my boyfriend for about a year we're both in our late 40s. The potential for undiagnosed ADHD came to a head about six months ago. He went from "no one has every said I have ADHD" to listening to the book and really relating to it. So we're out of denial, which is good but nothing much else has changed. Where it is really hard for me is in terms of plans- he regularly breaks plans we have together- usually because he has double booked himself or just completely forgotten altogether. We've talked about creating a "system" and he is doing a little better about adding things to his calendar. But even if it is on his calendar doesn't mean it is going to happen.  I'm working with my own therapist to learn that this doesn't mean I'm not important (some days I'm better at this than others). Today, I really got that he just can't do it. He's completely unreliable in terms of dates/times. He doesn't mean to hurt people, but he is. I've expressed my concerns and he says he plans to pursue a diagnosis and possible medication. How do I live like this in the meantime when it feels like the rug can get pulled out from under me at any moment and it feels hard to trust him? My instinct is to not make any plans with him at all- but that doesn't feel like a relationship. It feels like downgrading from a "boyfriend" to just dating. Any ideas?