Dunno about dating someone from church, don't really have any thoughts on that...
But, sincerely, it really is not fair for you to date anyone given where you are and insist on staying. Dating while separated and headed for divorce when DONE, sure, fine. Dating while married with no intention of divorcing, not OK.
Ask your C about the physical and emotional overhead of living like you've been living. Stress from the M could certainly start adrenal fatigue, but you'd be better if that overhead stress was really gone. It isn't.
I'll stop now for a few months, if you answer the question I asked about your brother and how you'd feel about him doing the same thing...