Rosy, your poor love.
Not only is this a digusting example of parenthood, but if my experience with an alcoholic parent is anything to go by, I bet somewhere you're still wondering how it's your fault and what you didn't do/can do to fix this relationship... It isn't and you can't.
Your mother probably feels so much guilt at not protecting you from it more, yet has stayed with him, that her pride won't ever let her admit it, so it's "your" fault IYSWIM. Plus if that text is anything to go by, she's managed to become the manipulator and emotional blackmailer that we usually expect the alcoholic to be.
I'm so sorry for you. I know how it feels to want to perfect family as a result, and then feel this big hole that the grandparents aren't part of it. That you will try and try for your kids sake, yet end up feeling like the hurt child over and over again.
We are told to "detach with love", I've never really worked out how to do this. A therapist once told me to cut ties, but as a dutiful daughter I couldn't.
But with a very kind Cognitive Behavioural Therapist, I have learnt (despite it still hurting) to step back from each row/situation/let down/lie and assess that it wasn't my fault. I think your GP would refer you if you explained how the situation gets you down.
I recommend reading "Adult children of alcoholics" - the synopsis alone will probably have you in tears of recognition at your feelings and behaviours, it did me. Also "Perfect daughters". Both available on Amazon, a bit american, but the principles are there. There are also adult children of alcoholics groups as well as Al Anon, which I'm sure you know about.
I'm really pleased you found a lovely man to share your life and family with, thank god I did too. It shows that part of us isn't like them, and they haven't taken too much away, because we could so easily have repeated that horrible pattern.
Godd luck honey. x