What you want to do is focus on your self-care very intensely. You have no control over how your boyfriend will respond — but you do have a choice about how you will respond. Please keep your psychiatrist’s appointment. You will want to take care of yourself for two good reasons. First, if this is a phase he is going through you’ll want to be in a good, or at least better, place when he is able. If he isn’t able to maintain the relationship you’ll want to be strong enough to manage. This will require you having as much support as you can muster.
Self care is the most important thing you can do during a time of relational crisis. This means treating yourself well by getting enough sleep, eating well and not doing things that bring you down. I’d devote my energy to the things you can do to bring you to and keep you in a better place. Your psychiatrist knows you and can be important in helping you through this time. Reconnect to your therapy and do everything you can to nurture yourself.