i have wondered that too. my sort of random thoughts on the topic, organized as best as time allows. : )
i believe this is one of those times where you have to really check your spirit and heart, more than waving the letter of the law.
while there may be grounds for divorce "legal" on technicality, i think that the bible teaches us that the spirit of the law is more important than technical obedience.
1) first question: do both parties adhere and participate in reconciliation?
i think the rebuilding after divorce requires two parties:
one who is forgiving and willing to examine ways he/she could do their part. willing to change and grow for the needs of the spouse. to fully re-invest where hurt and offense has taken place.
another spouse who is willing to do the difficult steps to rebuild trust. that means, a concerted and humbling effort to show even more transparency, communicate things that probably were never said, and put your heart and affections in a direction that might feel plain awkward or even forced. accept necessary guardrails that are designed to prevent this from happening again. i think the reconciliations usually fail become the adulterous one feels injured by the behavior prior to marriage and somewhat justified in their choice, and feels like the effort required to re-establish trust is far too humbling. it's unfair and one sided. the problem is, for all this to play out, along with sufficient distraction and time out for "events" can take a little while.
you could burn a couple years easily with two spouses who are doing their part but either not at the same time, or halfhearted. people who are more committed to their children, jobs, and interests as opposed to the work of the marital union. years of earnest effort made by one (or both) that fail for unspecified reasons, without ever achieving what was before the adultery
i could easily see how two to three years later, a spouse who was "cheated up" could say the following:
i have tried. OH how i have tried. i overlooked, forgave, and tried anew. i lost the "baby" weight, took up your hobbies and even burned my sweatpants. you tried for awhile, too. but soon, it was back to what things were like before. except now it's worse because i trust you even less than before. you never really came back. you don't tell me what you think, and you still keep too many secrets. are you cheating? probably not. but i wouldn't know whether you just learned from your mistakes and became a better cheater, or no longer care about such things, because you're not "doing it" with me. do you even love me???
you have become my roommate. and i'm now a fortysomething chick who is interesting and smart and wants a full life that you're unwilling to have with me. and i can take this hot body, education, and interesting life that i've worked oh-so-hard for and find someone who is crazy about me, wants to spend his time with. someone who he'll treat with more affection than his fantasy football league. someone who wants a God-centered marriage that fulfills intention of what fidelity and commitment both require and enjoy.
i want out. you cheated, and i tried again. but when you broke our vows, they became irretrievably lost. you can't say i didn't try. but now, i'm cashing and tapping out.
and let me just say right now, as a single woman who has never been married, writing all that stuff up there (actual stuff that i have heard first hand, not just once or twice...). oh so painful. never, ever, ever, God willing! but, i digress...
part of what i hate about the above is because it is ridiculously common (both genders have sterotypical stories) and technically it speaks to the fractured marriage from the point of when the adultery happened. i think the cheated upon spouse has the TECHNICAL freedom to leave and can present a very good case for that. but i really can't say what the spirit of the law says about those two.
at the end of the day, i still believe that two spouses who are WILLING to work towards any kind of resolution and stay in the marriage should be given the preference. i don't think we get to leave our marriage because we feel "unfulfilled". but that's my value (more than something i can biblically stand on) when adultery happened.
more points of consideration about exercising the freedom to exit the marriage regardless of time limit (or other factors):
2) you've elected to not separate and have re-established living as a couple or family. you're having sex and in a sense, re-consummating that which was broken. that becomes a point of consideration. it's one thing if you are unaware, but when you choose to re-group and soldier on, that is a choice.
OR as a result of the "re-consummating" your broken union, your family has changed. i can't exactly explain why (at this time) but i feel quite strongly that following the period of adultery and both have elected to stay in the union up to the point that child(ren) are conceived and born, things have kind of shifted. if you chose to stay. your family dynamic has re-established and grown. even if the child was unintended.
3) re-establishment of the affair, even if it hasn't been "reunited" but is clearly moving in that direction. in my opinion, anyone who has cheated with someone should be willing to agree to discontinue any/all contact with that person. even it it requires gaining a new job, or putting in rules to avoid that contact, for safety and the sake of the spouse who was cheated upon.
4) showing clear and undisputed evidence that they are establishing a new affair with someone else and abandoning the guardrails that were put in place prior to the adultery or after, in the attempt to rebuild the marriage. then, the previous cheating and pattern becomes entirely relevant.
i feel extremely inclined to point out that i've never been married, and i really don't know exactly how i would handle all these things. my strong opinions come from my complete admiration and longing for the ideals of marriage while aware of the fact that i grew up witnessing the carnage of several marriage failures and the pain (and fear, frankly) that came from the body of those experiences.
but yeah, those are my opinions with what i've seen and know. i have a lot of sympathy and compassion for those folks who have been put in such difficult positions. i have always said that because i don't believe in divorce, i wouldn't divorce a cheating spouse before i gave him ample time to repent and turn from that sin. however, i really don't know what i would do with an UNREPENTANT spouse. that is a whole different matter. i have often thought i would just separate and see what time/God reveals. but who knows. i can't really say for sure.
p.s. i want to make clear i wrote this as a woman speaking from my perspective as likely, the one "cheated upon". my decision to do so was not because i think men cheat more, or women cheat more. they both screw it up. thus, to be quite clear that none of my examples or words were intended to infer one bias over another. there has been a lot of pain felt by many christians who suffer painful marital events, and i realize that no gender has a lock on adultery, sin in marriage or depth of pain felt by spouse's choices.
edit: good gravy, this is long! if i had more time, it would be shorter. : )