Communication in a marriage is what makes it successful. What about sitting down with him and explaining that you are not feeling well and you are doing the best you can right now, that if you could do better, you would. Explain your guilt but also your inability due to the bipolar to improve until you get some help. That you are making strides in the right direction to get back on medication, that you need his support and love while you go through this 'down time.'Just be honest.