Nobody can threaten a marriage if it’s on strong ground in the first place. No matter who or what Paul is, if Sonny truly loves Will, he would be no threat to Will whatsoever. So, if he’s afraid Paul might take Sonny away, there is already trouble in paradise and he ought to be looking for a way to fix that instead of spending so much time and energy trying to get rid of him.
Of course we’d have no storyline if that happened so I guess we just have to sit and watch all this crap unfold while throwing pillows at the TV screen in frustration.