How long will it take our relationship to heal?
Probably longer than you think. Unfortunately, many couples try to shortcut the recovery process. Once the affair is confessed and an apology is made, these couples attempt to move ahead with "life as usual," even though the confession is only the beginning of recovery and restoration. More is required if full healing (a return to trust and deep connection) is to be realized.
The "recovery takes as long as the affair lasted" principle that has some general truth, but recovery time is different for every couple. The point of the statement is primarily for the unfaithful partner, who often feels like the work is done once a confession has been made. They need to understand that they've lived the experience for however many weeks, months, or years the affair went on. The betrayed spouse is only starting to process that reality, and it will take a LONG TIME to finish that work.
Here's the expectation I usually present to couples:
Start measuring from the point of full confession or last contact with the affair partner, whichever was most recent. That's you're zero-mark. (If new revelations or contacts occur, the clock starts over again.)
Even for short affairs (brief sexual encounters or something lasting a few days or weeks), it will probably be at least 6-12 months before you feel somewhat stable in your marriage. If the affair was longer (repeated contact or a history of infidelity), you can expect it to be at least 18-24 months before reaching that same stability... maybe even longer. This assumes that BOTH PARTNERS ARE INVESTED IN RECOVERY. If not, the kind of stability that results in renewed trust and intimacy will never be reached.
The affair is never forgotten. Years from now, something will trigger its memory, and the pain of it will be felt again. But they do the work, pain will eventually pull them together for comfort rather than push them apart.
The road to recovery is difficult. You'll have to endure a lot of pain to get to the other side. Your partner must exercise patience and care to help you get there. You'll have good days, bad days, and really bad days, but as time goes by, you will discover that the bad days diminish and the good days increase.