Well, I completely understand your worries when it comes to your kids, but well, maybe there are other things to look at as well.
Then, I worry about the kids having to deal with the emotions that come from dad not coming when he said he would, not coming at all, showing up drunk or leaving them alone on his weekends while he goes to the bar.
But see, all that will go on whether or not you stay together. You said that he doesn't come home now, he goes out to the bar.....he not where he should be now, and they, your boys, still have to deal with that plus the emotions of seeing their father drunk night after night anyway.
If he's been sober for five years and went back to drinking now and talking to him doesn't help, but makes it worse....I'd say that the choces are yours......do you want to live this way? So you want you boys being influenced this way? You have one that is coming up into that very fragile age group where they are faced with these decisions of drinking and drugs. It's just something to think about.
AS far as him calling you up in the middle of the night or coming over all the time....only you can allow him in or keep him out.
Have you ever been to alanon? If not, you might want to check it out. It's a start anyway, in learning how not to get caught up in the A's disease.
Welcome to this forum, glad to have you.