gh, what im telling you is this,
if you feel stongly that you need to know WHY she contacted om, then you have to be open and honest with HER about know she has. im not telling you to bet your chest and demand to know, you can still be loving and caring about it, but dont lie to her. tell her the TRUTH, you want her to so well you have to also. this is what i would say:
dear, i know you have been in contact with om, im not going into details as of how i know, but it do. i understand that there may be some unresolved issues between you two, but i need to know what those are, i does bother me that you have not told me you have been in contact with him, please im being honest with you about knowing, i am just asking you to be honest with me as to why you two are still in contact. thats how i would say it, but i am different than you, but when i promised my w i would be honest with her with what ever was bothering me i have to hold that promise, so please if you need to know the tell her the truth.