Lots of founders go through this. You should have an honest conversation with your co-founder. Probably couples therapy. One option is to do it with another founder who has been there (me).
You both are going through a challenging time. Of-course you are going to find some things that are more interesting to you than your founder, and vice versa. Especially if you are pivoting every month (which is a whole different problem).
Going through tough times can build resentment, the way to get on the same page is to talk.
Mediation is what you do when there's something to lose from dissolving the enterprise. But that's not the case here! Why preserve the relationship at all?
You both are going through a challenging time. Of-course you are going to find some things that are more interesting to you than your founder, and vice versa. Especially if you are pivoting every month (which is a whole different problem).
Going through tough times can build resentment, the way to get on the same page is to talk.