Well if he has not cleaned up the mess in a year and a half it is unlikely he ever will. It sounds like he has his life a certain way and thats the way he likes it. When you moved out he should have woke up and made the changes you had a problem with, the fact that he has not shows that either he does not take your concerns seriously or he simply does not care.
I wish I could tell you that with time he will change........but this is not a time issue. As for his ex wife, you have a valid point in requesting she not behave in such a way. As for the friend, if he has no where else to go it is unlikely your boy friend is going to simply toss him out. And the kids, yes they are old enough to be on their own but many parents allow their children to stay regardless so trying to make him put them out isn't likely going to work.
The fact is you must sit down and look at this for what it is, he has continued allowing others to interfere in your relationship regardless of how that makes you feel. You need to decide what you want and go talk with him. Do not put up ultimatums.....they never work. But you can explain to him how you feel and how this is hurting the relationship. Ask him if he would be willing to set time limits to get some of this resolved. Such as the kids find their own apartments within 6 months. As for his ex, maybe he can set some ground rules. Such as she is not welcome over to the house unless A) She has been invited or B) She has called ahead and requested to come over. Limiting these visits to no more then twice a week would be helpful. If she wants to spend time with the children she can do so in her own home.
As for the old friend, you may be stuck with that. You can not ask that he toss his friend out in the streets. You can ask that he set some boundary's such as how the living arrangements are or even request that the friend begin looking for a new place to stay.
The fact is all these things can be done, if your boy friend is willing to do it. If not then it may be time to look at this for what it is and see that if he does not love and respect you enough to consider your feelings then maybe this relationship is not what is best for you.