Jeff, mc is right, you have to tell him the truth (tailored for a 5yr old of course).

I told my 5yr daughter that her dad wouldnt' be living with us, that he will be seeing her often, but that he wouldnt' be in the house like before, that he decided to be on his own. That we both loved her a lot and that we were still a family, her brother, her and I and Jesus, there were 4 in the house. Gave her a big hug and told her I was so happy to have her.
At first she was quiet and told me she didn't know how to feel about that (code for she didn't like the sitch) but now she stopped talking about dad not being home.

In your case I understand is harder for he misses her (my d5 doesn't miss stbx, for she now realizes that when he is around I wont' be). More of a reason to talk to him and have him understand that mom doesn't live there anymore, just telling him she is working and she'll be back soon prolongs his longing and his hopes are up that any day now mom will be back as usual.

Do it for him, tell him she has her own place and that he now has two families, (I know, why the hell anyone would bring grief to these little angel boggles the mind) and that he is very very loved by both of you.


Be not afraid...I will repay you for the years the locusts have eaten Joel2

30something
2kids
survivor of S, MLC, A, D
I have peace in my heart, at last.