Frank's and Matt's paths cross, they get to know each other. The more Frank spends time with Matt, the more he likes him, but at the same time he subconsciously starts to find something common between Matt and Billy and expect Matt to be insincere and betray him. So Frank tries to push Matt away (probably hurting him in the process), and Matt proves that he can be trusted time and time again.
Happy ending after all the suffering would make me happy :)

+ Frank doesn't acknowledge his irrational mistrust at first.
+ David and/or Curtis try to bring Frank to notice his trust issues.