Reggi,

What are you afraid of?  That he will get back with her?  That she is “better” than you?  That he thinks of her rather than you?

Have you had anxiety issues beyond this ex, i.e. have you been anxious about other things?  Are you generally an anxious person?  Are you normally insecure in other situations like with work?  etc.?

Have you talked to him about what qualities that you have that makes you desired, wanted, and a good partner?

Mark