If your husband is having a hard time letting go of a past love then the two of you may need to consider counseling. He needs to be able to talk about his feelings and get them out in the open so he will be able to leave them behind.
Try to look at the situation objectively to be sure you're not confusing your own possible feelings of insecurity with your husband's alleged attachment to his ex-wife.
If you have tried telling him how it makes you feel to know he can't get over her, then give him a choice, either he does what he needs to do to get over it, or you will have to leave.
