you have a rough situation. I made all the same mistakes and more. It ate me alive. You have to back off for your own sanity. You have to find your own happiness. This won't happen easily, or overnight. Find the inner you, the strong and happy person and focus on that.
Your H is a cheater. No need to look at the GPS tracker, if your H isn't home it's probably safe to assume where he is. Loving partners are home in bed every night, not out, leaving you to wonder where they are.
Teach yourself to stop reacting emotionally to everything he says and remember the DB rule "Believe nothing they say and only half of what they do". He is full of $%!+. Don't let this crazy guy dictate your reactions.
I hate to say this, but your H most likely been doing worse things and for longer than you know about. Just prepare yourself for this.
My biggest piece of advice is this: don't believe something just because you want to believe it. I did this so many times, and when I read you say "I can't believe this is happening", you made me think of this idea. B/c we can't believe it's happening, we tend to believe the wrong things - we want things to be better than what they are.
You can do this. Even though you don't know what you're doing yet (saving the M or moving on), the path for you is the same.
H 34 W 29 BD 3/12/18 Divorce Busted Spring 19
It is not things that bother us, but the stories we tell ourselves about things.