Something to keep in mind when it comes to sex, that helps a lot with insecurity about past relationships and what not, is to think of sex as 2 separate "skills" (like if it was an RPG and you had a "sex skill stat"). 1 skill is just general sex knowledge and is what most people think of when they're concerned that they're inadequate in bed. But there is a lesser known 2nd skill that is much much more important, which is your sex knowledge with your specific partner. Imagine you have a sex stat for every single person you've ever slept with. At the start of a relationship, everyone is going to be low on that skill, and you build it by communicating and having sex with that specific partner. Your general sex knowledge can give you a head start, but nothing will replace building up and learning that intimate language with your partner that is different between every person.

With that in mind. Some things to consider

-A vibrator is your friend, not your enemy

-Getting in your own head about your performance is just gonna make your performance worse, it's a vicious cycle. Try to just have fun, and if you cum too early you can always switch to oral or hand stuff. There are lots of ways to please a woman.

-Maybe press her harder about if she is really satisfied. If you suspect she is just placating you, ask her something like "I know you said everything is perfect, but I really want you to have an amazing time in bed, and I can't give you that if you aren't honest and we don't work at it together, so I just want to make totally sure"