Here we go again!

I can yo-yo diet like nobody's business. Can anyone else relate?  But recent events in my life are forcing me to an understanding that I won't be young forever, and if I want to keep up with my kids, I need to get serious about losing weight and being healthy.
It started a few months ago, when my 75 year old mother (who is 100+ lbs overweight) started having health issues.  To make a long story short, her weight and pulmonary issues make her a high risk candidate for a surgery she needs.  The doctor said she could die on the operating table.  I asked him if she lost weight, could he reconsider doing the surgery.  He said yes, but for the short term, she has to live with her health condition.  Her condition causes her to be unable to walk without oxygen, urinate on herself, or worse poop.  
While not all of her issues are due to her weight, some are, and it is an eye opening experience for me.  I am 45 with a 5 and 8 year old.  I don't want to be unable to enjoy life with them when they're in their 20's or 30's.  
So I think about all this when I want that sweet or that chip.  Sometimes it works and sometimes it doesn't.  I really need help for the times that it doesn't.
So here we go again, and I don't want to yo-yo anymore. I want to get this right.