You seem to be suffering from performance Anxiety. Due to overthinking about your ability to satisfy your partner, your performance goes down, because sex is a mind game, needs to be done under relaxed state, not under any pressure or tension.
Next Steps
Whenever you go for sex, tell your partner that you are not going to put your penis inside, you are just going to enjoy foreplay. You can do foreplay for 15- 20 mins, whenever you feel enough confident, you can put it inside