I (F31) feel like I over reacted by leaving my BF (M37) after he was in the car with a different woman

I (F31) have been with my bf (M37) for 10 years (12 total but we took 2 years off after our kiddos was born).

Thursday night he went to hangout with his friend to have a drink while I stayed home with our kid. He ended up running into some other friends of ours/mine while he was there and they called around 1:50am to let me know he was drunk, could barely stand drunk and also stated he was there alone as the friend he went with had left a few hours before (12am) and there was a girl hanging around him/them basically all night and stuck around once his friend left.

She said that he could barley stand but refused to go with them but their Uber was there so they needed to go and sent me the address.

I arrived at the location where he was since he drove and I didn’t want to risk him driving and he and this girl are in the back seat of his car. His head is on her shoulder and she’s somewhat holding him, and his pants are unbuttoned but he’s completely out of it. The girl said she was trying to get him home safe but didn’t know his address or any phone numbers to call to reach anyone.

He claims it was nothing and I have this disgusting gut feeling that it was more than what he’s saying. Like why stick around at a bar when your friend leaves if you weren’t there to hang out with that chick? I broke things off immediately but I’m having second thoughts and feel like I may be over reacting. (I did reach out to the woman and she did not respond.)

UPDATE:

I spoke to the other woman (FINALLY). She confirmed they have in fact met up but have not been physical just coffees and lunch and then that night. She said it’s all fairly new they began talking on social media in early April but didn’t meet up until last week. She said they were going to go back to her cousins house but he was too drunk and she wasn’t sober enough to drive so she helped him in the back of his car while she tried to find his address. No explanation on pants being undone. She did say she knew about our kiddo because he talks about him but she had zero clue that I was even in the picture and was super apologetic (don’t believe that because the platform they talked on I am literally all over). Still way more than I even care to deal with at this point in my life.

Thank you guys for your kind words and advice. It’s been a super stressful and emotional 48hrs.