You need hobby and job, gives you purpose and direction. If you are financially stable, a hobby could work. You should also eat out occasionally, exercise, go to movies, park, just have fun. I'd also suggest to get in touch with those kids, have them visit and spend quality time bonding in or out of the house. If the situation requires you not to be around them alone, invite the father and keep it casual and in good spirits. Do something to breath life into yourself.

"Time is the most valuable of currency, don't waste it on sorrow, better to spend it happy."
(I now live with evil person that is trying to kill me through verbal abuse and it's psychological effects that branch there from. This person had shattered me into something dark but I shed my face of frown to a smile knowing the sunrise and the song will always be there. I live in a prison but a prison can only trap me physically, my decision whether it takes me emotionally. As said, spend time wise, not for misery but for joy.)

Best of luck