***MrP's pre-post disclaimer - I'm not a therapist; just a guy who spent some QT in therapy, reads a lot, and experienced a relationship troubles a time or two who is offering some peer-to-peer feedback. Consult with your IC for professional guidance.***

I agree with Boat that something brief and tight like "W, for some time now we've been disconnected and it doesn't work for me. I no longer want to live this way and I 'm going to file D. Let's talk about what that would look like" is best. I try to give myself no more than 3-5 complete sentences when having a difficult conversation like this that needs to be focused. Maybe:

1. I continue to feel unhappy with this marriage right now.
2. I want to be in a relationship that (briefly describe 2-3 things that are crucial to you and without referencing W or using the word "you" about her) OR something like....
3. I want a partner who fully loves me and my children, and will actively work to maintain put a relationship with me first.
4. At this point, divorce is the best option for me.
5. I need to talk about what that would look like, especially for (insert kids' names).

Note that my suggestions are all focused on YOU and solely on your needs/wants. Nothing like "OUR" kids, "OUR marriage" or "your drinking doesn't work for me". You're articulating what the standards are for any partner who will be qualified to be in a relationship with you going forward. In theory, it reduces the likelihood of an "attack" response because you aren't directly criticizing or provoking her (quick shoutout to the chapter in The Solo Partner that discusses blame; I DID retain some of what I read).

Now, certainly she can say "OH AND CLEARLY THAT'S NOT ME" or "WELL I GUESS I DON'T MEET YOUR LOFTY STANDARDS MATURIN", "OH AND YOU'RE SO PERFECT' or something similar. People who want to fight, deflect, deny what's happening, feel like they've lost control/power over you, etc. will find a way to try to bait you into the conflict. You job again is to not tak the bait in the trap and calmly stick to your guns:

1. Everything I stated is about my needs and standards in a relationship going foward.
2. Divorce seems the best option for getting my needs met.
3. I recognize this decision can be a shock.
4. If not is not a good time to talk, I hope (later today, tomorrow, or some other option in the next day) will work when a conversation might be more productive.

And then exit the conversation...which means you'll likely want to plan the conversation for a point in time that best enables a clean exit and/or reduces the opportunity for W to follow you while trying to continue to ignite conflict. After a similar conversation, my W followed me to my office and, when I shut the door and locked it, tracked down the spare key (so, also, hide spare keys).

My recollection from reading MANY posts in this forum is that, at this point, you've got to be ready to D. It doesn't mean it will happen or that you may never R in the future if by some miracle W has an epiphany. You do have to be at a point where if those standards above aren't met or if the life you'd be living conflicts with your values, you will walk (and keep walking). Otherwise your words are hollow.

I know you've got an IC so I'd recommend working with them to confirm the feedback you're receiving from us armchair quarterbacks is right for your sitch. I always worry that something I suggest might not truly be best because we're only getting half the story in this forum.