Hi Feyth! Just read through your situation. You are in a horrible spot right now, but hope is not lost. You're doing a lot of things right, but the first thing you need to realize is that fixing things will take time...way more time than any of us want. Really acknowledge that fact, and take a deep breath. Now take another, and another...just be for a minute, okay?
Okay, hopefully you've untensed a bit, slowed your heart rate and breathing, and feel a bit more relaxed. Your H has complicated matters greatly by seeing someone else. The absolute worst thing about this fact is the flood of excitement going through his brain right now, via our trusty friend serotonin. He's likely feeling excited about OP versus feeling like he's done with you. It's an uphill battle from here.
What you have to do is focus on being the best you that you can. Find the truth in his complaints and start working on those things. There's not one of us who cannot improve in some way. The goal is to become a person only a fool would leave. WAS usually don't notice anything we do until we truly begin to detach...for some reason, they can sense us pulling away, and it is often enough to get them to start thinking about what they're doing. But honestly? Detaching is usually the hardest thing for most of us. We love our S and want to fix the marriage, not pull away!
Be aware of what you're facing. This takes time. Your heart will bleed. You must focus on you for now. Detach as much as you can. GAL activities help keep you sane. I highly recommend working on the goal section of DR as soon as you can. Having a plan helps a lot.
Doing this self-work is working on the marriage, not just you. You want a better marriage, right? Not the one that just fell apart? DB is not for the faint of heart. It is hard work, takes time and commitment, and is emotionally taxing. The fact you're still here after lurking and realizing the work involved is fantastic! I'll keep checking in.