Wel, in the case of an affair (especially when there are kids involved, there's my modified version of Gucci's 2 step approach:

"You want to be with OP? Fine, get eff out of my house"

Then proceed with step 2.

Me 35/XW 33
S13 & S12
M: 10/17/98
OM & S: 07/08
D final 06/09/09
12/03/09 - 06/13/10 "Piercing"
06/13/10: Engaged to Re-marry 10/17/10
06/25/10: Expecting baby #3 2/14/11