My Dad Told Me He's Having/Had An Affair

Hi there,
I'm new to this forum, so I'm going to try my best here...

My parents have been married for 28 years.
My mom, unfortunately, had a brain aneurysm six years ago.
She needs a lot of assistance walking, eating, bathing, bushing her teeth and getting dressed and primarily uses a wheelchair.
A family friend of ours comes by and helps her out Monday through Friday from about 10 in the morning until about 3 or 4 in the afternoon so my Dad could run errands, do yard work, go grocery shopping, etc.
This woman has been there for my mom for almost three years now. She cooks her breakfast every morning, she bathes her, she makes sure she's okay... when she has a medical emergency she always comes over and helps out.
She's been wonderful to my family.

She and my father have always gotten along very well, but it was about a year and a half ago I started to realize that it could be possible they're more than friends.
They joke around a lot, they message each other on Facebook all night long, they text with each other (my dad rarely texts anybody).
My father likes to drink, he's a severe alcoholic and she doesn't mind drinking with him.

Finally, tonight... My father-- drunk, told me that he had an affair with this woman.
He said he was sorry for it and said it was a horrible mistake.
He said he ended it and they're just friends now.

The problem that I have with this is that my cousin told me that she caught them doing something (kissing or hugging, I'm not sure) about a month ago.
My father told me that he ended his affair with her awhile ago, or at least that's what he made it sound like.
I'm lead to believe that they're STILL having an affair.

I'm kind of in shock right now.
My mother has lost all of her independence, she mostly sits in front of a tv all day long and does nothing, while my dad is out doing whatever the heck he wants to do.
She does not have the capacity to speak up, to voice her opinions and stand up for herself.
She's completely defenseless... and all of this is happening right under her nose.
Before she had her aneurysm, she stood by him, covered for his drinking several times, provided for him and for my sister and I... and now, years later, her husband of 28 years is cheating on her... WITH THE WOMAN WHO TAKES CARE OF HER.

I'm in absolute shock at the moment.

He said he hasn't had sex or compassion in six years and she was coming on to him.
Her husband is awful to her and she's miserable in her own marriage.

I'm very torn, I'm incredibly upset and I'm very, very angry.

I'm sorry for rambling, but this just happened tonight and I needed to get this off my chest and I need to talk to someone about this.

I can't tell my family, because that would ruin them, I've only talked to my best friend about it so far tonight... I figured the internet would be the next best option.

Thank you very much for reading, I look forward to your responses.