On a more practical level, I suspect you may still feel guilty about treating her so poorly and have yet to forgive yourself. Examine your feelings. You may find that the issue is still unresolved within yourself.
Otherwise, explore what assurance you need from her to fully "believe" her when she tells you that her commitment to you hasn't changed. Sometimes, I need extra attention and affection in addition to the words.
Best wishes for you and your family.