Holy shit, their marital relationship is so very much none of your business. Your Mum's venting to you and sharing intimate details --like how your dad is now impotent-- is wildly inappropriate.

Do you really want to think about your father's erections? Do you want to think about the details of how your fathers turgid penis used to regularly enter your Mum's vag, but is no longer?

No? Uncomfortable? Then why are you letting your Mum inappropriately vent this info to you, her daughter?

The end piece here, and I'm sorry to have to point it out, is this:

In 2012, Dad was diagnosed with prostate cancer. He had surgery, which turned out to be pretty extensive, but he’s in remission now and looks to be all clear.

Even if it hasn't metastasized, your dad's 5 year survival odds are abotu 50/50. Prostate cancer is a bitch. The odds are that your dad will die in a few short years.

He might be more aware of his odds than you or your oversharing Mum. Facing your own probable end, in a shitty, painful manner, plus the fact that you're no longer able to fuck your own wife, would be enough to drive most men to drink themselves drunk as regularly as possible.

I'm astounded at the lack of empathy you and best-friend-mum seem to have for the self-medicating response taken by this man whose body has been ravaged and who, given the odds, will probably die a horrible death, soon.

"OMG my husband will no longer fuck me! Also for the rest of his life he'll have to worry about a horrible disease returning, it likely will in a few years, which will mean his end will involve shitty chemo and the loss of his own body functions. But he's getting drunk regularly!"

JFC, you and your mom. Have you never seen anyone else die of cancer before? IT SUCKS. Ever have a disease that prevented you from fucking?