Once I realized that I had failed in my goal (a 3.5 or so my first year), my life was pretty much drained of meaning, so I withdrew into my mausoleum and waited patiently for my life to end and the pain of existence to cease. I kept making halfhearted efforts to function, but my life no longer had a mainspring to drive me.
Maybe you need to re-examine your definition of success. In all honesty, I don't see a high GPA for its own sake as a particularly worthy goal or a real accomplishment, and certainly not something that you should allow to drain meaning out of your life. I studied very hard during my sophomore year and got a very high GPA. Then, after I'd had some sleep and time to distance myself from things a bit, I decided that it wasn't worth it. The lack of sleep and the emotional roller coaster were too much, and I realized that there was more to life than driving myself mad in pursuit of a high GPA for its own sake.
When I hear of other's successes, it always feels like someone has punched me in the stomach, because it reminds me that my life ended a long time ago.
If your kids are young, you can't be too old to change your life and do something that has meaning for you. Lots of people make changes in their 30s and beyond. But (and this is only my opinion), the only person you should be competing with is yourself. You will always encounter someone who is better than you at something. That's life. I tell my kids, "Even if you win a major marathon, you can be sure that there are kids in eastern Africa who will run faster than you, in bare feet, over rocks, in hundred-degree heat. So don't waste your energy worrying about others when you really need to focus on improving your own performance." There are times when competing is bad for you, and making yourself happy is one of those times.
It's very hard to engage your family when you feel completely ruined and are devoid of any kind of purpose.
What would give you purpose in life? Can you find a way to attain your goals? If a career change is difficult for financial reasons, can you start small and do something outside of work for a few hours a week that will make you feel good?
Just wondering: you sound very unhappy. Do you need help from a therapist another neutral person you can talk to honestly?
