Well first off, stop chatting with the FB friend.
You are only 4 months out from Dday. Your emotions are still going to be up and down. Even very, very down.
The last thing you need to do to yourself is get involved in an online EA.
It is not fair to you and it is not fair to your WH, if you start looking to another man to fill a void in your life. Either you want to give your M a chance to heal or you don't. If you want your marriage to heal, then you need to turn towards your WH to fill your voids.
Talk to your WH. Without listing off everything he did wrong, just tell him how you are feeling. Tell him you feel down. Tell him you need to talk more.
Go to DearPeggy.com and look at the statistics she has on infidelity. The couples that talked the most about the A and where the BS got their questions answered were the ones most likely to survive.
Do not assume your WH is psychic. You have to tell him what you need. Don't yell it or scream it. And don't try to make him feel bad when you tell him. Just calmly and plainly explain what you are feeling.
IF he still refuses to support you, then you have some decisions to make.