For me, it took a long e-mail to him detailing how unhappy I was, followed by months of couple counselling, then getting clarity (through individual coaching) on what I need out of a marriage/relationship (which was similar to what I was already offering - commitment, trust, transparency, partnership etc) and then asking him for it. It was clear he couldn't/wouldn't give it to me.
Asked myself if I was ready to live like I was living (very unhappily) for the rest of my life. In which case, I'd have had to stop moaning about it. Answer was no.
It wasn't a reckless/overnight decision and I'm 100% satisfied that I gave it my all. It's hard but I know it's only short-term and there's light (even if distant) at the end of the tunnel. If nothing else, there's some relief and a sense of control.
I strongly believe that we only ever have 4 options when struggling (in marriage, work etc) - Change the situation (by asking for what we need), Shift our perspective on the situation (learn to look at things differently), Stay and Moan about it (be the victim), or Leave.
I would say I tried the first 3 options, then finally chose to leave.
Hope that helps. Best wishes to you - whichever way you go....x