Uh oh, the next episode is going to change a lot in the Mac/Jo relationship. At least for some time.
I'm sure it'll all pan out in the end of the episode. After all, the episode's title is 'misconceptions'- that may be the overall theme of the episode. The producers have already expressed their intention of making the Jo/Mac-friendship stronger. A fight or misunderstanding between the two of them is a non-coventional way in doing so, but it still is the more realistic, and effective one.
I think Mac's reaction to Jo comes from the fact that he feels as if he is being cornered. Jo's suspicion is about to reveal the secret he desperately wants to keep to himself. In the end, their misunderstanding of one another's intentions may force them to verbalize their positive feelings towards each other- and in doing so, indeed, making their friendship more solid. That's how I see this storyline evolving, anyway.