Although I haven't read your sitch, helping her a lot financially sounds enabling to me. If it were me I'd help where the kids were concerned and pull back in other areas. If she's with OM then he should be helping her out. For Christmas I'd buy the kids gifts from myself, possibly get her a gift, and let her take care of her own Christmas.
You don't sound very detached to me. I'd plan something really fun to do on S's birthday (go out with friends and have a great time!).
There is no arriving, ever. It is all a continual becoming.
