I don't want to sound silly but I never realized how much I loved this woman till now, she is probably surprised I haven't divorced her yet, she knows me very well.
No one was more surprised than me that I didn't go through with divorcing my cheating WH. On DDay, I came out of the gate swinging for divorce. I knew I was going to confront him when he came home and I knew that he'd spent the day with an OW. I'd made dinner and made sure he ate before I started talking, because I knew he wouldn't be able to touch a bite after I was done. Weird, I know. Then, I just told him that I knew he'd been cheating, that I didn't care to hear any of the details, and that we would be getting a divorce. He gave me his best hang-dog look and agreed it would be for the best, then scrambled away to go text his girlfriend. We had agreed that I'd find us a lawyer and he'd split the banking, so a few days later, I asked him if he'd done it yet. Turns out that he didn't really want a divorce, and could I give him thirty days to prove that he could be trusted? Well, we'd been married for more than thirty years, and I hadn't found a lawyer yet, so I said, "Fine, but here's the deal... there has to be absolutely no contact with the OWs". Of course, it wasn't more than a couple of weeks before I busted his ass in contact with an OW, the one he'd been future-faking with, trying the "let her down gently" approach so she wouldn't hate him. At that point, I gave him about thirty seconds to decide if he was "all in" or "all out" or the marriage. I was done. I wasn't going to put myself through any kind of back and forth. He ghosted her that day.
I tell you all this, not because I want to influence your decision, but because, like you, I was utterly shocked to find out that I still loved my spouse. And like you, we'd got together young. I'd had the care of him since he was 18 years-old. I didn't know what would happen to him without me but I was already witness to the kind of crummy choices he was capable of making. Things had gone pretty shitty between us for a long time. In a way, he'd put a giant bullseye on my forehead where he then directed every ounce of his middle-aged angst and disappointment with life. His view of me had become parental, like I was the authority figure keeping him from having any fun. The hateful disrespect he directed at me was that of a rebellious teen with a full grown man's resources. And yet, when push came to shove, he didn't want to go. And it wasn't just about the things he'd be losing in the divorce. He was afraid of losing ME.
Our R went gloriously well for the first couple of years. He moved Heaven and Earth to prove he was all in, right up to and including transferring his job out of state, selling the house, and moving away from the triggering scene of his crimes. The last two years we've been struggling because he's not working communications to my satisfaction. Real change is rare, and communications hasn't stuck for him. But our R is still serviceable, if not as joyous as it was. In R, we tend to go through a re-bonding period which is very similar to the early infatuation of courtship and lasts for about as long.
Like I said earlier, no cheater is owed a second chance. So, if your inclination is to divorce, you're NOT wrong. Your WW's behavior was, as you've noted through the response so far, heinously disrespectful. She is not deserving of a second chance. No cheater is. A second chance is a gift, one that you give or withhold based on what YOU want. I do disagree that your cheater is "the worst". My WH spent my birthday that year fucking an OW, then came home, handed me a card which read "hope you find your happy place" with a stale plate of store-bought cheesecake. Then there was "your wife is a c*** day". I saw videos of him fucking her in my vehicle, the same one I'd taken my kids to school in. The OW who came to my work place pretending to be a customer. The plan for coming to my house wearing a disguise just to taunt with her presence. Countless, cruel jokes at my expense. It was like he'd turned into a mean teenager, a bully. But there's a REASON why they put the BS down like that... and it's because if they think about who we are, what we are to them, they can't go through with their dirt. They have to demonize us in order to achieve the mental gymnastics necessary for continued cheating. Which leads us to what they're getting out of it.
Once an affair gets going, the cheater is receiving a biochemical cocktail of feel-good chemicals. Risky behavior cranks up the adrenaline. Oxytocin, released during sex, promotes pair-bonding. Neurotranmitters readjust with norepinephrine rushing in waves, serotonin lowering, and dopamine rewarding the brain. The behavior becomes addictive, and upping the risk results in greater rewards to the brain. So, you begin to see why they keep at it, even when the adultery has become a threat to everything they had. This is also why they twist themselves up and demonize their spouse in order to keep it going.
Don't get me wrong. I'm not defending your WW. I just want you to feel like you have choices. Yes, her behavior was disrespectful and toxic. But the same can be said of every cheater. Adultery, in an of itself, is an act of disrespect, no matter the trappings which go along with it. The cheater respects no one, least of all themselves, as they toss their integrity aside for some cheap-ass chemical high.
I can't speak to D, but I can tell you that R is hard. The dirty little secret of R is that, "yes, the cheater gets away with it". When we take them back, we insist on new boundaries and a real change in the cheater's character. But there is no punishment. Once you've come back together as a couple, you can't punish your cheater without punishing yourself. You don't have to forgive, per se, but you do have to write it out of your ledger... and that's a hard ask. Your situation IS recoverable though if that's what you want. Do spend some time thinking about it before you commit though because the road is long and hard. Like you, I was surprised to find that I still had love left and that I still cared what might happen to my WS.
I can tell you this much regarding D... we have lots of wonderful people who have pulled the ripcord and made better lives for themselves. At 44, you're still a young man and this might be an opportunity for you to explore the world as a single man with complete freedom. In terms of trust, whether you R or D, it won't ever be the blind, naive trust you had in youth. But that's a good thing. Henceforth, your trust will not be given lightly. People will need to earn it.
Strength to you as you process.