As a person with bipolar and a person who has been on both sides of this kind of situation (in different relationships), I can see where he is coming from too.

You are expecting a relationship where you text and talk on the phone frequently and he is not up to that at the moment and is getting a lot of questions from you about how he has withdrawn as a result. If many things look to you as "excuses", I wonder what these conversations look like to him. It sounds like you are blaming him in your mind for the current state of your relationship.

About boundaries, those are mostly about what one's own expectations and actions will be. Not so much about the other person.

This doesn't look like a short term situation even if it is related to an episode because in bipolar the episodes are recurrent.

If you continue in this relationship expecting him to change then I think you are going to be even more disappointed in the outcome.