If the Horse Is Dead, Get Off
If you don't have a strong intuition to light your way, how do you know when the not-so-great-but-maybe-good-enough relationship is kaput? The answer lies in what you want and need, in the compromises with which you choose to live, and in the hard choices you're able to make. You answer the tough questions by knowing yourself, acknowledging your obligations, and living by your values.
Sure, you'll want to discuss these issues with him, but his responses are just one source of information. Your best decision will come from looking as deeply into yourself as you do the relationship.
Examine your history. If you usually want to back out at this point, you may need to stay longer and risk coming closer.
When you see your part, and you're either unwilling or unable to do what is necessary to improve things, or if your efforts are insufficient and he's not able to make up the difference, you know the romance is dead. Leave? Well, maybe.
If you have children the obligation to provide them with the stable scaffolding they need to become solid grown-ups with rocky romances of their own may mean that you'll never openly declare this union over and gone. Your decision to go or stay will reflect your core beliefs about parenting, money, family, social status, a permanent New Year's Eve date, and all those other difficult issues that we iced over with the buttercream of being in love.
If you decide to cut your losses, I suggest you create a vivid, positive vision for your future. See it, say it, meditate on it, write it down, flash on it at every red light. When you catch yourself thinking you're too old, too poor, too weak, or too needy to make a change, laugh in your own face.
Letting go hurts. But staying, once you've decided the relationship is really over, means being buried alive. Face your decision with courage, kindness, and a galloping leap of faith. Joy is waiting.