Is NOBODY wrong in the post ? POST : Last one was deemed shit-post, lemme start over.

I walked in on my boyfriend of 6 weeks in bed with another woman Friday morning. He kept apologizing, trying to offer an explanation, wanting to hear the whole story,claiming she was just his ride to work the next day since his jeep is broken (which is true) etc. Followed by gaslighting for making me question his intentions. I blocked him, everywhere. Obviously there wasn't much more to it I needed to hear.

I believe his actions, regardless of intent or what actually happened, was influenced by heavy drinking the night before. I drove him to the bar MYSELF before going to work (I work graveyard shift in a hospital lab). He was meeting a friend to watch hockey, he claims this girl was his friend's daughter (so they know each other) who drove him home because he was too drunk. The next morning I saw them lying next to each other. In hindsight, this may be the second time, the first on Christmas Eve, a woman walked out the back door when I got home from work, although banter between he and his roommate the next morning suggested it was his roommate's hook-up. In this instance, I asked him who she was when I found him in bed naked, he said he didn't know and "I always sleep naked"...did they both fuck this girl?? That's gross. Anyway, I didn't see whose room she walked from. I think something happened christmas eve as well, he just didn't remember. He once told me the morning after sleeping with me "i don't remember anything, I just know I had sex". Gross.. layers of gross...

I don't know how he thought I would take it or if he even knew what he would be waking up to the next morning, either way I was pretty upset. One of them could have easily taken the couch, so he either cheated, intended to cheat, or was too fucked up to make any rational decisions and know what he was doing.

The time we were together, he would get into beer and liquor from getting home from work until passing out. He went to bed with vodka and lemonade at the bedside. He drinks and drives constantly (even with me in the car, which I voiced as an issue) and goes through pints of whiskey in no time. Now it has ended the relationship and I am tempted to tell his father, whom I have only met once and who I was told to say nothing to about his drinking and gambling. 

I want to forgive him and move on. Besides, even after "I love yous", and me practically living with him the time we were together (which makes it even weirder he let me witness that) I want to move on. However I am worried it will be viewed as prying, petty, or my intention would seem misguided.

Tl;dr should I tell cheating ex's father about his alcohol abuse, or would it seem petty?