I have been seeing my boyfriend for almost 4 yrs .bt he's married to the mother of his kids & has been for 24 yrs . He keeps telling me he wants to get a divorce and has all the paper work to do so. But he keeps putting it off ? Why doe it seem like he doesn't want to go through with the divorce?

Maybe he is happy the way it is. Having you on the side and his wife too. If you let him keep coming back then he will do so until you say no. Then see what happens.

Tell him it's over. and move on.
He is playing you, for sex, and with his wife, too.
He has both worlds, you and his family. If you can keep living this way, then do nothing. If you are waiting for him to divorce his wife, it probably will never happen. You can find someone else. I do wish you the best.

He has no reason to get a divorce. He's got you! You sleep with him, you love him, he's got the dream existence. Not only that, but his wife will sock him for every penny he's got, especially if she stayed home to raise kids, and especially if any of them are still under 18. And third, his kids are probably old enough to speak their mind, and may have told him that they will have nothing to do with him if he divorces their mom.
Time to end this...