AITA?

So, my boyfriend recently bought me a car (as in yesterday) and while we were about to leave to go to the dmv to get it in our name, he said "damn" while looking at the girls ass. For the record, hes never behaved this way, and has always been respectful. I asked him what that was about and he tried to play it off like he didnt say it but hes a horrible liar and he knew i could tell. He hasent said sorry, but i didnt make a big deal at the time bc i really wanted the car. I figured id give him a week of peace as a thank you for the car, but i cant stop thinking about it. 

For reference ive always been a chubbier girl bc of my PCOS, and have always had a hard time with my health and losing weight. The girl however, didnt seem to have that problem. She was fit and tbh, that ass was fat. But its a respect thing. He can say what he wants while im not there, but control yourself while i am yk? i figured id bring it up in a week after ive had time to think about it, but its brought back a lot of insecurity ive worked through in the past. 

BTW, im not going to break up with him. Weve been together for 2 years, and have had an amazing relationship, and still do. Hes very attentive, takes care of me amazingly, etc. I believe if you try to leave someone for every little thing, youll never find a happy relationship. I just dont know what to do. Should i get over it? or should i bring it up.