Most Helpful Guy
I think you are asking too much... it is 100% possible to platonic friends with an ex. Unless you have past issues regarding cheating or lying then you need to learn how to trust you dude. Have faith in him that he is a good person and wouldn't betray you. You simply should not dictate who your significant other is friends with. It is not a good foundation for a relationship. I understand your concern but it is just bad business to start saying who a guy can be friends and can't be friends with simply because of your own insecurity.
Besides deleting her number really does nothing right? He could write the number down elsewhere, memorize it, or she could call him so in reality it on creates a superficial sense of security.
TRUST HIM until he proves there is no reason to, but unless he has a shady or sketchy history with you regarding honesty (whihc you haven't mentioned) then you shouldn't treat him like a untrustworthy person. Otherwise you may create an environment where he feels like he has to do things behind your back because you have unrealistic and unfair expectations