Do you love this man?
If so, draw up some guide-lines, such as he buys half the food you and he eat when he is at your place, or contributes in some other way to your joint expenses.
Likewise, make it clear that his son is welcome at stated intervals for a meal, or to stay for a day or so once or twice a year, but not just to come, expecting to stay at the drop of a hat.
It sounds to me that these men are doing what is crudely known as sponging on you, so if you don't love him, kick him out now.
If you do love him and want a future with him, I would suggest telling him, he is welcome to see you, but you will not live with him until he has finalized his divorce.
Are you really sure, he is divorcing his wife, or being divorced?