Ending a relationship is hard. It's even harder when the relationship hasn't quite reached the point where you are so fed-up (or exhausted or angry or frustrated or hurt etc etc) that you rarely second guess yourself because those emotions can be quite strong when you are at a certain point.
So maybe you aren't at that point - yet. You do see where this is heading and you do know it's not good for your kiddies.
I also get the - I have the house and a comfortable life thing. I have wondered sometimes if that is the time someone chooses to leave because once you are all settled and some of life's struggles are out of the equation you go, ok, so why am I so miserable, or why do I wake up wanting to cry? Is this my life?
I don't know exactly what that might be for you. The loving care of a fully involved partner? Peace and contentment in your home?
In the long run you are doing him a HUGE favour. They won't see him drunk as they grow up, while he might not be "sober" he will at least not be truly drunk.
I think it's totally normal to have these feelings, it's a big, big life shift. Also being away and coming "home" could trigger those feelings perhaps. Getting home after a holiday is great. You have also had time away from home to relax.