Katie,
You will not be able to move on as long as he is in contact with the OW. If you are to salvage your marriage, an absolute, non-negotiable, no contact must be put in place, and this should not even be a question. What good is the 3 months going to do if he is talking to her still? Do some 180's and make yourself that person that he finds amazing, and that he wants to be with. But you must make the changes for yourself, not him.
Shock


Edited for your protection.