As a step parent to a SD10, I can relate. Your W is his mom and the anger will subside. Don't bring up OW or W to him, enjoy your time with him and try to change the subject when and if he brings them up. Been there, made that mistake already.
Glad your IC session went well!


Me(W): 29 EXW: 30
T: 6 M: 2
SD: 10
BD: 04/2016
PS: 04/2016
W officially "seeing" someone 09/2016
W filed 03/2017
Officially Divorced 11/2017