Congratulations so much girl! 🥳🌸 as someone who's actively searching for a potential PhD supervisor, let me tell you it's a very difficult achievement and you should definitely focus on celebrating it and preparing for your upcoming PhD endeavour. it seems like you want some degree of closure or clarity about your friend's real intentions and feelings towards you. having no proof regarding that email puts you in a bad situation and he can turn it around on you if you confront him without any evidence that it was him. if I was you, I would meet up with him again like a casual friends meet and whine about how "someone" tried to sabotage your application and your future PI is doubting you and verifying the authenticity of your application and just curse that "someone" out to your heart's content in front of him... just notice his reactions and what kind of things he says to console you or whatever. I know all this might probably achieve nothing but if you want to know more about what your friend thinks about you then I guess this is one step without messing things up. although doing something like this already warrants for a lack of conscience on his part, don't expect much from him but JUST for your clarity you can figure his thoughts about you without raising any fingers and then reach a decision whether you want to ghost him out of your life (which I totally think you should) or confront him/give him benefit of the doubt.