As stated, click on phone (or computer) and choose move, then chose kick out. Make sure that he is the only one. You will know when it asked is this your family? And it shows who you want to stay in the house. That sim should not be in the picture.
What I suggest is that you save before you kick the sim out, in case you click on the wrong button.
If you want to know where that sim went to, follows them to their new home, if they are given one. The sim I kicked out, unfaithful husband, I followed him to the "pre-fab" home, basically a trailer. Big change from the mansion he had been living in.
As for questions, I am still full of them and they haven't kicked me out of the forum yet,
so I guess you are still safe with asking more questions.