I joined a gym, but after going for a few months
I just gave it up.
You can't just give up on yourself, as getting out, and doing things will add a touch of variety to your life, that insures your happy, and balanced.
Maybe now the kids are very dependent on you, but trust me, as they grow up, and start school all day, you will have a lot of time to do your own thing, and enjoy it, so hang in there, and don't quit on yourself.
You are responsible for your own happiness, so be creative.