Okay, obviously we are going to have to get you away from thinking about performance in order to have you relax enough to maintain an erection like you always have. And before I tell you what I recommend, let me also normalize your experience - your gf did a number on your head with her reaction because every guy has an occasion where he either cannot maintain an erection or else will not be able to finish. Fatigue or alcohol usually play a role, but usually the next time the guy tries, everything goes well (unless the spotlight gets focused on the erection, which is what happened to you).
But the "fix" is going to involve something called "sensate focus," and it is a technique specifically designed to take the anxiety out of the sex act. It is also successful almost every time, so here is how it goes:
(1) The First Stage of Sensate FocusIn the first stage, the couple has two sessions (this can be one, unless the anxiety is really high) in which they take turns touching each other's body, but with the breasts and genitals off limits. The purpose of the touching is not to be sexual, but rather to establish an awareness of sensations both while doing the touching, and also while being touched by their partner. his way, there is NO PRESSURE to become aroused or to orgasm.The person doing the touching is told to do so on the basis of what interests them, not on any guesses about what their partner likes or doesn't like. The couple is instructed that if sexual arousal does occur, they are NOT to proceed to intercourse.It is also recommended that this first session is as silent as possible because talking can detract from the awareness of physical sensations. Of course, the partner being touched must let his or her partner know, either verbally or nonverbally, if any touch is uncomfortable.(2) The Second Stage of Sensate FocusIn the next stage of sensate focus, touching is expanded to include the breasts and genitals. The person doing the touching is instructed to begin with general body touching, and NOT to immediately move to the genitals or breasts. Again, the emphasis is on awareness of physical sensations and not the expectation of a sexual response, and intercourse and orgasm are still prohibited. No pressure, right?The couple is asked to take turns trying a "hand riding" technique as a means of nonverbal communication. By placing one hand on top of the partner's hand while being touched, one can indicate if he or she would like more or less pressure, a faster or slower pace, or a change to a different spot.Oh - also, these nonverbal messages should be conveyed in such a way that the person being touched does not take over full control, but simply adds some additional input to the touching, which is still primarily done based on the interests of the toucher.
(3) The Third Stage of Sensate FocusIn the next phase of sensate focus, instead of taking turns touching each other, the couple is asked to try some mutual touching. The purpose of this exercise is to practice a more natural or real life form of physical interaction (people don't usually take turns touching and being touched), and to help each partner shift attention to a portion of his or her partner's body and away from watching his or her own response. Couples are reminded that no matter how sexually aroused they feel, intercourse is still off limits.
(4) Subsequent Stages of Sensate FocusThe next stages of sensate focus are to continue with the mutual touching, then at some point to move into the female-on-top position without attempting insertion of the penis into the vagina.In this position, the woman can rub the penis against her clitoral region, vulva and vaginal opening regardless of whether or not there is an erection.In a subsequent session, she may progress to putting the tip of the penis into the vagina if there is an erection, all the while focusing on the physical sensations and stopping or moving back to non-genital touching if either partner becomes orgasm oriented or anxious.After completing a session or two at this level, couples are usually comfortable enough to proceed to full intercourse without difficulty.
Now, also remember that steps can be combined in an evening if you are both comfortable, but I think you should at least set up the evenings (or daytimes - whatever!) with some spacing intact so that YOU feel more in control. I hope she agrees to this; it will be successful because it takes the pressure off of you. If you are satisfied with the response, please hit "accept." That is the only way I receive credit for my answer. Thanks-