Any answers?

My husband has bipolar depression and when he gets in a mania state on day 3 of no sleep he starts accusing me of cheating on him and really believes I am with men in front of him and other stuff. What is this and why?

This may or may not be related to the Bipolar or any meds that he is on to treat it.
I suppose that after 3 days of no sleep, my own thinking would not be in good form either.
Is he aware that he is doing this afterwards and how hurtful it is to do this to you?

I could only guess that it may be 'delusion' or hallucination from lack of sleep. He needs to speak with his primary doctor or pharmacist (chemist) about this.

Bipolar is tough. It can be controlled to an extent in some cases better than others. He needs to stick with his med dosage regimen and not use other drugs or alcohol.

This is a peer-based, support forum. We do not offer professional services or give diagnosis. The solution to this sounds like it needs to be determined by his primary professional team.
Best of luck to both of you.