I want to know how :

1. He moved out, moved in with another woman, AND introduced him to his own mother and YOU were completely in the dark about all of this?
2. Why aren't you talking with his MIL? Have you confronted his MIL NOW about her enabling his infidelity?
3. Why on earth aren't the two of you in FAMILY THERAPY?

Individual Therapy is NOT going to solve MARITAL problems... I have argued on this forum earlier many times that IC can OFTEN make marital problems WORSE...

You need to update your signature with the FULL status of your husband.. is he living with OW? On his own, living with his mother?