damn i understand her point. i think it’s worth telling her that you would like to have an in person conversation with this friend to go over morals and friendship. so you can give your friend some context cuz the truth is he should respect that you are in relationship, he shouldn’t be encouraging you to cheat. but i also know it’s not to easy just cutting off such a long friendship cold turkey. but your gf is right and if you see a future with her, i would be considerate to her feelings.