Dear Flossy73:
I ask these questions to understand your situation and question better, so to be able to give you input that I hope will be helpful.
Does he keep only her emails or is he in the habit of keeping lots of people’s emails?
Did your boyfriend express anything to you about age, her being young and you being older?
Did you ask him “why he would keep in contact with someone who didn’t think he was good enough”?
anita