Infidelity makes it even harder, IMO. I used to be convinced that RAH was cheating and it would tear me apart. (I just didn't know her name was Bud Light or that she often answered to Jaggermeister
)
When I found my mind going down that awful path I learned to stop right there & ask myself, Can I control this? One I fully accepted that I could NOT, a huge weight would release & I could then focus on, "OK, then what CAN I control?"
Which brought me around to self-care stuff. I COULD get enough sleep, even if it meant taking natural supplements for a while to force my body into the habit while my mind still resisted. I like the chewable melatonin tabs you can take without water because if I woke at 2am with Pain & Panic, I could pop half a tab & drift right back to sleep. The better sleep I got, the more my health improved, the more my mind cleared. The more my mind cleared, the better care I took of myself (diet, exercise, etc.) the better/earlier I was able to see myself walking that path in my mind & stop myself sooner.
I also started spending 15-20 mins really thinking hard about the things I had gratitude for just after waking (before getting out of bed) and right before closing my eyes at night before I drifted off to sleep. Slowly, bit by bit, things got easier for me because I felt much more in control of Me. Good luck!!