I can relate to what you're going through because I am going through the same process. When is enough enough? Have I really done everything to build a stronger marriage with my spouse? How will we know when it's time to finally move on?
The fact is - we are strong or are working towards that goal. We are capable. My C was taken by surprise when I mentioned that I am deserving of a marriage that is full of hope, optimism, passion and unconditional love and that I will have that someday. Preferably with my W - but I will have that kind of marriage regardless. It's really the first time that I have mentioned that I might be the one to make the choice to call it quits - that the choice does not exclusively belong to my W.
Spouses like mine run an inherent risk by sitting on the fence - thinking that love is just a feeling and waiting to see if that feeling comes back before committing to the marriage again. That risk is that IF the "feeling" comes back to them, we may not be around anymore - we will have chosen to move on with our lives just as we have chosen to love them unconditionally. It's a scary thought - but empowering at the same time. And we also have something that our spouses don't - a place like this to exchange thoughts and ideas, to give a sympathetic shoulder or a whack on the behind with a rhetorical 2X4.
I will - we will - come out of our respective situations fine regardless of the outcomes. We hope that it will be with our spouses. But we are strong and we will be fine...