Maybell, I don't think it really matters that much whether you ask him in person or by email. It sounds like this issue is a bit of a trigger for you (fair enough) in which case the advantage to email is the ability to construct it carefully and thoughtfully and so you can avoid getting pulled in.
H 37 Me 36 Together 15 years Married 5 years No kids BD Apr 2014 H moved out 2 Jun 2014