Someone, I can't remember who, said this process is not linear. You will make strides for a while, and then backslide. Of course the strides get bigger, and the backslides shorter. We all do it. Don't beat yourself up.
With respect to her son, if I remember right, he's 15ish? I'd have a candid talk with him, explain that you love him, and want to spend time with him. I wouldn't throw his mother under the bus, but make sure he knows YOU are not abandoning HIM. It won't be too long before he's 18, and can spend all the time with you he wants, regardless of what his mom says.
M:23 T:26 Me:53, Wife: 60 S:18 D:16 filed 7/16 W moved out 4/28/17