Am I over reacting?

My SO & I have been together 15 years, we have 2 beautiful awesome children together - 14 yrs old & 10 yrs old ☺️
This past Friday we went to a party for my sister, he disclosed that he didn't want to go but I made him anyways... We knew we were going to go hunting the next morning so to keep the drinking & staying out late very minimal. 
We get there & immediately start enjoying the company then this woman enters... He says he knows her from high school, even though he never mentioned it before! The group starts to karaoke & he totally starts to show off. Literally dancing in the middle & was like the king of the party. Okkkkkkk, I get it lol but then he starts to dance & sing with this 'woman'. I go to the bathroom & when I come back into the living room, he totally backed off. Ok. I go into the kitchen & try to enjoy the company there. My best friend & I then go talk on the back deck & she says she's concerned. It's evident that him & this woman are really enjoying themselves. Ok. He then comes out to talk to me & I tell him what she said. He said he knows her from high school & that he is just enjoying the company as in the party. I said it  time to leave & he says ok, call your dd. So I go back into the party & everyone is leaving to the bar. I take this time to leave the party too & walk to my dd. He never noticed!!!! 🙈 I give him an hour, I'm an idiot. I literally then have to drag him home & tells me I thought you left? 
I feel so embarrassed, I feel absolutely ugly & that I'm no body. Worst feeling ever. I know the alcohol played a lot into this but why am I being accused of being jealous? Over reacting?