I understand your pain and feelings of betrayal....and I really know about the sleepless nights and sleep deprivation. My sleep cycle has not recovered yet.
I found that the sleep problem makes everything 3-30 times more emotional...and depending how you handle your emotions putting off certain conversations until you had a chance to get a couple of hrs of sleep may help. I wouldn't make any big decisions in that state that you may regret later. In that zoned out state I had to fight hard not to be reactionary....something to look out for.
The why question ....good luck on that and hope you believe it if you get one.
Are you convinced his dick didn't find other fun places to visit ....I think this could be the reason for all the lies. How or why does he have a fuck buddy if he can't get it up? ... you may want to .check with her and see if that's true...the whole limp-dick-man idea.... the way your story started I'm surprised she didn't say he was gay also ...
Good luck ...try to get some sleep D