I don't think that it's possible to be on good terms with an active alcoholic unless you're doing, giving and saying exactly what they want at that moment, and even that can change at the drop of a hat. You are being completely reasonable, but all he's likely to hear is that his alcoholic lifestyle is being threatened. He will come out fighting. And its unlikely to be fair.
You say You can't afford to get a solicitor. I'd argue that, given the experiences of most, you can't afford to NOT have one.
I'd also suggest getting some emotional support from people who've walked your path. Have you looked into AlAnon meetings in your area?
I reckon the folks over in the friends and family area will have some advice that will stand you in good stead as well...
https://www.soberrecovery.com/forums...ly-alcoholics/ and if you haven't read the stickies over in that area I'd say that now wouldn't be a moment too soon.
Wishing you all the best for a smooth disentaglement.
BB