There's a phrase that comes to mind when people ask why I decided to get divorced: It's the little foxes that spoil the vines. Basically, it's a lot of small things that built up and built up and turn into a f*ckup in the end. Atmosphere at home the last few months was miserable and I didn't want to be at home. Also found out that she was having a thing with another dude while I was busy with the purchase of our "family home." I ended up having a thing with someone else when I decided that I didn't want to be in the marriage any more and even though I was technically cheating on her, she did it first. I had already gone to see a lawyer to find out everything I needed to know about possible outcomes for everyone with regards to the divorce.
One Saturday I told I her I was done and that I couldn't be in the relationship anymore. We talked for a few hours and decided that it was best for the kids and for us. I started with the divorce proceedings and it went pretty quick after seeing my lawyer the second time. Things actually got better between the two of us after that and we thought we'd be good friends moving forward. Then my pension paid her part and things went South really quick. She basically turned into the wicked witch of the West and I cut off all communication where it wasn't about the kids.
We've found out about a lot of stories she's been spreading about me/my now wife in the last three years, which is not fun but proves to me why I should've gotten out of that toxicity a lot earlier. As much as I hate the phrase, everything happens for a reason, it rings true in this regard.
If there is any piece of advice I can give you that I want you to seriously think about - Your mental and emotional health is really important. If the relationship is causing issues with either of these, perhaps it's wise to move on. I wish someone had given me that advice a few years earlier.