I’m a supporter on this forum and don’t have PTSD, but I think that may be a good thing in this situation.
How you’re reacting to what’s happened and is happening is completely, 100% understandable and normal. You don’t have to be suffering from PTSD or other disorders to react with panic and soul crushing fear to something like this. Lying, cheating, betrayal are all forms of abandonment which tear open the oldest, most vulnerable parts in all of us—the need to feel safe and belong. Once that has been scared, we’re in free fall. Panic and anxiety is a natural reaction to that, no matter how stable you’d be otherwise.
I could tell you all day long that this is no good and you need to leave, but I don’t think that’s what’s most important right now. Most important is that you figure out, step by step, what it is you need that can supply you with a sense of control and safety elsewhere. The strength you gain from providing that for yourself will help you make a grounded decision that feels logical and organic to you. If you can, in any smallest way, take the focus off of him for small increments and redirect it towards yourself.
What is it, you think, you need to take the first steps in that direction? If you’re a reader, is there literature (or audiobooks) you can research that would be of interest to you? On healing from abandonment, on learning to trust yourself? Are there people you can reach out to—therapists—with whom you can feel vulnerable and feel a sense of connection with?
Small steps build on one another, you just have to start somewhere and take one day—one minute—at a time.
Most people on here would say that betrayal and cheating isn’t enough to qualify for developing PTSD and I’d agree...to a point. This is a trauma and I think the after effects of it very closely mimic a post traumatic stress response. Don’t underestimate what’s happened to you, be compassionate first and foremost with yourself.