Cant lose my virginity, please help

Im writing this on a throwaway laying in bed going out of my mind because I cant understand whats wrong with me.

To shorten things, today I’ve (20M) “tried” having sex with my girlfriend (19F) for the first time as we’ve been together for some time and wanted to try it.

Basically, for the first time in the same day, things got heated and I’ve put on a condom, everything was fine until the moment I tried to put it in and my penis went soft. Same thing happend again about one hour later. And same thing happened again the same day only few hours later.

I don’t know what to do as this is not the first time this has happened, this also happened to me once before as I was hooking up with a random girl and got soft, a few years ago and tought nothing of it, tought maybe it was performance anxiety or the fact I was drunk, but the fact it happened 3 times more today has killed me and I can’t stop thinking about it.

Is it PMO? Whats the problem, please help…

TL;DR: Got soft 3 times in the same day trying to lose virginity with my girlfriend while putting on a condom/putting it in, happened once before aswell. HELP