Another new guy with problems exploring the act of making love

Hey reddit, I come to you in a time of need with questions. They have probably all been asked and answered here before, but I need advice that I feel is written and tailored for me, if you would be so kind.

Last week I gave away my virginity to a girl who has had her fair share of lovers. This came after a long period of talking over a couple of months, so I feel I know this girl very well. Though yet both times I have gone soft right before she had orgasms, and this is making me feel weak and useless, and her sad for not being able turn me on throughout the entire act (even though that is not the case, I find her tremendously attractive). She also finds it hard to talk about sex, so I have trouble getting info out of her about what she likes and not, though other personal topics float freely both ways

So the main problem here is me going soft when were in midst of the act, what can cause this, and more importantly, how do I prevent it? This is a serious fucking threat to this relationship, and I really hope for this to work out.

On beforehand, thank you for reading this, it helps writing it down.