Renee, Never "assume" anything w/him. He may or may not have been w/the ow. But, that's something you can't worry about and/or control.
He most likely asked where you were because he was going to talk to you, nothing more. Don't over analyze the situation because you aren't going to find the answers. Why? Because he doesn't know why he does what he does himself.
Okay, go back and read your posting....you aren't going to give him anything because he told you weren't welcome at his house. You do not stoop to this level. If you are trying to work on things, you do the opposite. Yes, he would expect you to put up a fight about things...what do you do....the opposite. You've got to work on your anger a bit and come to realize that you'll get more with sugar than you will with vinegar. Just because he says and does hateful things doesn't mean you have to do it too. Two wrongs do not make a right.
Yes, you did good this time. Find an outlet for the anger and frustration. Take a long walk, kick boxing or beat the crap out of a pillow, but do not show that anger to him. He's the one that needs to grow up and you, as his friend, companion and wife, do not need to get into the sandbox w/him to fight it out. Step back, allow time and God to work on him.
Keep the focus on you and your son. That's all you have control over right now.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.