“Michael moved in with a woman, and they had several children together, and yet he refused to divorce Terri and allow her family to care for her.”
I think Michael refused divorce as revenge for Terri’s dad speaking up for Terri so much, plus Michael wanted to save his own butt by hiding the truth.
Keep in mind that Mikey used TERRI'S MONEY, not his to kill her. He would later turn down millions of dollars to let her live.
My belief is that he was terrified to let her get better. His quest to murder her began after they got the money AND after she started to improve.