Pause, Relax & Recharge. This happens and in a way it is good that your co-founder is going strong and doesn't need a break too. You badly need to recharge you

Pause, Relax & Recharge. This happens and in a way it is good that your co-founder is going strong and doesn't need a break too. You badly need to recharge yourself & this has to be time well spent cautiously and consciously chalking out what you do during your break. A hackathlon or doing some sales for a friend can charge you back it need not be necessarily travel or rest. In effect you need to do something very different from the type of thinking that you do everyday (note different in thinking not the work type). Also give yourself a break from all the headaches on your current startup - consciously keep away from talking to anyone on the team or checking out updates (positive updates are probably fine) If you are the type of person for whom physical exertion works free up the mind - go for a hard trek or run or swim. As far as your depressed nature, cofounder resentment etc - you might be blowing it out of proportion right now given you are not able to contribute effectively or thinking too much.