Did your DH really bond though? I know when my DH had his fling, he did it with someone that he had no emotional bond with whatever. And, despite what I'd always assumed about affairs, he found the sex revolting. In fact, he took out a lot of his anger at himself on her, subtly, but also struggled to cope with seeing his shabby standards reflected back at him in her - but part of him was out to damage himself, so he felt that was all he deserved.
What he got out of it was the one thing that was missing in our relationship - time together. We were ok for sex, but I remember him saying that he felt the sex with her was expected of him (and he took something because he physically wasn't attracted to her) and basically thought "all I have to do is ejeculate, then I've got someone to listen to me".
I suspect she didn't enjoy the sex either, and that her motives were more to avoid being single than borne out of genuine feelings for DH.
And for several months afterwards, I fell apart because she'd been so unpleasant to me and my DC's. The one email she sent to me referred to my children's physical/mental safety, and several months later, she followed up threats to these by frequent communication. That she knew about me, that my time was filled with dealing with child's SN's, that she contacted me to make nasty observations about my child's disability during her few weeks with DH....yes, I probably obsessed with her for a while. That she could give me such hatred while helping my DH destroy his marriage, and no, she didn't know that I knew what was going on. In fact, having a stranger threaten to harm your children is what probably cracked me up. It's so against how I could behave, and to put a 10yr old child in counselling because of it, it is tough.
And, of course, she'd had a DH who'd cheated on her, so part of me was thinking that she knows what it's like to be on the receiving end, so how could she? Alternating with, now DH has told her it's over, will she be truthful (no, she just tried to inflict more damage on Dh's family).
That there's not been a lot of time between the Op's DH's fling and now is probably why she feels that she can't trust him. But if her DH is genuinely supportive of her and genuine about his reasons for staying with her, that trust will return. We're 2 years on, now. And I could see from my DH's behaviour during the fling (when I wasn't supposed to know!) and when he finished it, and since, that he's genuine. We've got a much more balanced relationship, and this last year has been brilliant.
I still struggle to cope with things like the OW knowing he wasn't going to work (because he was with her - some of the time, and using work as an excuse to avoid her the rest, but still not going to work! He was trying to destroy everything in his life. So how could she have supported this? But then I think she's so emotionally unaware on many levels that she just couldn't see it).
What bugs me is that she knew him and knew that his behaviour was out of the ordinary (threatening to harm his kids, then demanding physical affection from me, not going to work, lying, he was cracking up - and we know the reasons why, and he's addressed them). And it was her that pushed for commitment, made his solicitor's appointment etc.
I actually pity the OW now. She's leapt into another relationship within weeks of DH telling her to clear off. And, as with DH, I'm sure she was declaring love within days, ready to move in with him within weeks etc etc.
But, that's her problem. And until she addresses it, it will continue to foul her life. (so if I wanted revenge, she's doing it for me!). In the same way, OP's OW is in a situation of her own making. Nothing to do with OP. And OP, it might help to think of it as her now getting the hurt/inconvenience that she might have been inflicting on you. Karma? And leave it at that.