The bit I really need help with is that my husband’s girlfriend keeps emailing me over him seeing the kids, saying it’s unfair and that he’s devastated because he feels he’s lost them.
I’m guessing she’s writing out of guilt and maybe your husband is also giving her a hard time over the kids and she thinks it’s in her interest to try to patch things up.
It’s driving me mad because this has nothing to do with her; what I actually feel like discussing with her is why she started an affair with my husband and wrecked our family in the first place.
You don’t owe this woman anything and it’s not your job to make things easier for her, so tell your husband that you’d appreciate it if she didn’t contact you.
It’s a hard thing to do, but it’s the right way to approach things and it will benefit your children in the long run.