Male 18 years old

So a few weeks ago I had an embarrassing moment. Alone with my GF who I haven't had any kid of sex with yet but I am very attracted to. I feared I may have performance anxiety as whenever we are somewhere public even a kiss will get me hard as stone, but when I think I may have to use it my dick becomes completely unresponsive. And what do you know, I get alone with her but cant get hard. Were making out topless and over about an hour she tries to pull my pants down multiple times but I have to stop her and say "let me lead" meanwhile shitting myself in my head only worsening the issue. Eventually I just got triggered and left.

This all started when I failed to get Hard for my X girlfriend after fucking her about 100 times already. This happened because I watched a bunch of porn and cummed right before she came to my house, however the moment has scarred me ever since. The embarrassment I felt that day is still affecting me today and I think I must have performance anxiety.

Question is how do I deal with this? Its definitely not porn induced as I only masturbate about twice a week max. Shall I try and buy some drugs in the UK to get me over it or can I somehow fix it without the need for drugs as I'm 100% sure its all in my head

Any help appreciated, thanks