Obviously I'm not in you marriage , nor can I say I know 'exactly' how you feel, but from your post, splitting up sounds like madness. It really comes across like you're treating divorce as a fait accompli, that you see any improvement to be impossible. Kind of a negative and half-arsed apporoach to yours and your children's futures if I may say so.
There are loads of threads on here from women whose husbands have had an affair, but who are fighting tooth and nail to save thier marriages, partly for themselves, partly because their marriage, and eg the last 18 years deserve it, and partly for the kids.
You say you love him, you say you have a lot going for you. Instead of limply saying in your heart of hearts the feelings you had won't come back, maybe you could put a bit more urgency and importance into this?
Why won't they come back? Have you tried? What have you tried? Agreeing to go to councelling is a positive step, but starting something with negative views and half-hearted intentions isn't exactly ideal. Ever heard of self-fullfilling prophesy?
Why do you think it would be better to split? Better for whom? I'd say your and your children's financial and social and status, and happiness would all take a BIG drop. Statistiaclly after divorce men's standard of living goes up about 30%, whereas a woman's drops by 25 - 30 %. Being a single mother to 3 young kids would be enormously difficult. This would stay with them and you and your husband FOREVER.
My advice to you is to do EVERYTHING in your power to improve your relationship. When your kids ask why you divorced, surely you'll want to be able to look them in the eye and say it was the only way, that you did everything you could to save your marriage. These are the promises you made to your husband after all. Sounds like he's prepared to put in the effort, but doesn't sound like you are tbh.