I honestly think that's the best advice you can give in these cases. Getting proof only serves to hold it against them, and that, in my opinion, doesn't help improve personal relationships.
I agree with Nemo and Kynes, it's better to win the girl back than to fight with useless arguments.
Regards!!
P.D: Kynes, sorry for editing your post, I wanted to quote you and I didn't realize it :lol: