There's a lot of sage advice on this thread. Before you have the talk, treat this like a business and get your financial and legal ducks in order. You don't need to have everything ready to be executed, but you should educate yourself on all aspects of splitting. On the financial side includes retirement savings, properties, pensions, expected inheritance, family heirlooms, extravagant gifts, and even credit card reward points. On the non financial side, think about adult children living arrangements, pets and even how you're handling mutual friends. On the actual splitting up side, you should educate yourself on all the ways of getting a divorce legally. Most cases this would start with a long period of separation, complete with separation agreement of assets and then going to a judge to get it signed off to execute the divorce many months later when you prove you'd lived separately. This means you will need to work out how you're live (in different rooms in the house, who's going to move out, etc). In those cases, you really want to get your legal ducks in order so you aren't accused of abandoning the home.
Here's something I learned going through my divorce and watching those closest to me go through it: Shit never goes as planned.
It took 3 or 4 years longer than expected because while we were going through all the right steps to getting split, those conversations become incredibly soul baring and intimate in nature and you might find yourself talking to your wife or her talking to you like you've never done before. Regrets pop up. Sincere apologies creep up. Unsaid wishes get said. My relationship went through a two year re-honeymoon phase where we re-fell in love and that was really unexpected from both of us. In the end it didn't work out for completely different reasons on why we decided to go down the 'research on how to get divorced part' and I wouldn't trade that last two years for anything. My best friend who is like a brother to me went through something similar, where everything was green lit on both sides to split and they took one last vacation together to see an aging relative and ended up taking a 5 day extended tour of the country to come back home committed to making things work. My uncle one day told his wife who stopped having sex with him he was unhappy and he needed more sex. She said she wasn't interested in sex anymore but told him to go find a girlfriend. He was unsure about that route until one day his wife came home with a widowed girl friend of hers who wanted a booty call. They now all live in the same condo building as neighbors and I'm pretty sure he's been faithful to that arrangement for some time. I think its' been about 20 years with that arrangement.
On the other hand, my sibling initiated a divorce with a man who was completely blindsided (he actually though everyone was happy and content) and it's been 15 years and he still hasn't recovered. I talk to him a few times a year and go for beers and he always always tells me he wish he had some warning signs or the chance to go through at least half a year of counselling together. My sister never ever once told him she was unhappy with something. She stayed silent and then pulled the trigger. I asked her if that was the case and she admitted she never told him she was unhappy. To me, that's not very fair. You own it to the partner you chose for life at one point in time to have that discussion and see how they respond.