Hi Agbo, first have you been masturbating to porn, if so even though you getting a good erection, I think that you have porn enduced ED, so what you need to do now is take a sex break a sabbatical from all sexual contact for 8 weeks, try explaining that to you g/f, but its the only way to go, this will reboot your body
So for you its no masturbating, no sex or sexual contact, no oral sex, you need to be truthful with your g/f,as this is your only way forward for a new full sex life, look your g/f will not like it one bit, its up to you now.
Good Luck
well try to stay away from all this and start looking only on videos ad porn site and feel what you are feeling. may be this can help you.