You don't need to kick her out, but you can tell her you are not going to live in an open marriage where you are sharing your wife. You can tell her that if she is going to choose, and I stress her choice, to date another man, then she needs to move out and your son will be staying because you want him to be raised with good morals. And dating other people while married is not good morals and quite frankly someone making very bad decisions and bad choices. Again, her choice. You cannot force her to do anything.
