I would not suggest viagra for someone who has no physical issue, it's use is mostly for people who literally cannot get it up, whether high/drunk or because they have a medical issue. Mental blocks need to cleared by person who are trying to sleep with. You do need stop thinking about it so much when you are in the situation, the more you think about the more anxiety you get the worse it will become. You need this new girl to do what your g/f did and pull you through it.
His issue is mental and sadly it comes down to the girl, she needs to be reassuring and relax you, if she doesn't you will struggle and don't use viagra because it will become you have to use and you don't need to. You need to explain to her the situation, relax but she also needs to do things that make you relax. You managed to get it right with your ex so i assuming she was reassuring and she did something to help you.
I explained it to her, and like I mentioned she is really understanding, the bolded parts is almost exactly the advice she gave me, but for the life of me, the more I tell myself not to think about it and to just relax, the more I seem to think about it
With the previous girl the anxiety and fear never came to this high point, the first time I got over it because it wasn't as bad, this time round it feels much much worse...Thanks for your input though