How long does the devaluation(sp) last?

I did not know when mine started all I know is we had a fight and that was it. He left did not talk to me for a month just left me and the kids. I knew when the honeymoon faze was over. But not the devaluation part. A couple more questions also when he emails and ask about the kids he always brings up our first month together how he really liked it. That was his favorite time with me. Also do they really love the kids at all? Also how can some narcs marry and stay married for years?