First, be honest.
Tell your hubby when and how the feelings occurred. You must be willing to expect a reaction but be prepared, stay calm, and try to negotiate the continuum of your marriage if it lasts. Chances are, no. It won't. But there are ways you can make you and your hubby feel better:
1. Be mindful of the pain you have caused. Letting your hubby grieve will be best for this kind of condition and do not try to buy him on false promises you cannot deliver and are not certain of.
2. Give him space. This is a lot to process and he needs time to be well again. Don't rush him.
3. Stay a friend if it is something he wishes. Being supportive may reassure your hubby that though, you no longer love him, you do care about him.