Why does Kevin gets angry with Adam at the end of episode 2 when he's in that house?

Kevin was angry because he found the UNKNOWN's phone that had Adam's contact on it - he was going through the phone to see if there's anything on it.. and he said there's one thing.. "YOU!"

The red texts that popped up for you to select was Kevin texting through UNKNOWN's phone, to verify that you got the text when he asked "Adam, you got it right?" And along the lines with how can I (Adam) be working with this person (UNKNOWN) and felt betrayed, because he trust you (Adam) all along.