Is it normal to cum fast with new partners?

OK so lasting with my ex is really spotty. Some days im a two pump chump and then others i can make her cum 3x a night. i dont know what causes it and its really frustrating, its either i got "it" or i dont. I tried getting my mind off it but I either lose my boner of its just not that effective. Like i said i either have it or i dont. I'm really comfortable with her to the point where my boners arent as hard as they should be.
now im having sex with other girls and i cant last at all. its extremely embarrassing to be honest. the first time i got head i lasted 20 seconds, same thing after that with a different girl. now this 3rd girl came around, and i would stick my dick inside of her ONCE and i would explode everywhere. I'm not even nervous around that girl, I dont overthink or stress about cumming too fast it just happens.!!! I'm also rock hard with these new partners, don't know if that matters. This is a really frustrating situation because i want to let go of my ex and spread my seed(just kidding) but I'm shook and kinda traumatized to go out there and hook up with girls. what can i do. by the way this is all sober, when im drunk or high on drugs i'm a beast regardless. i dont think any of my friends have this problem so what the hell, how do i last longer with new partners?!?! why do i have to have this problem UGHHH