I want so badly to fix him and I just can't and then I feel worse
We CANNOT fix others. It is not our JOB to fix others. just as no one can fix US. when we start looking at our partner as a "rehab project" of any sort and have a desire to CHANGE things about them, then we have slipped from a partnership to something else.
his prime directive is to KEEP DRINKING. and he found the easier softer way to do that. he isn't choosing the new woman OVER you or the kids, she's just a means to an end.