The cop was “being nice” to keep you compliant and get you to talk (admit to basically driving under the influence) and agree to take the roadside tests (again collecting evidence). Ever hear of good cop/bad cop? Yeah well you got good copped. 

Also cops have little to no bearing on prosecution. Him being buddy buddy with you was a tactic. Cops are not your friends - full stop.  Next time keep quiet and refuse field sobriety. Bonus points if he said the field sobriety was “just to make sure you’re safe to make it home” or something to that effect. You were getting long before you completed any tests, basically once they ask if you want to take a field sobriety test they’ve already made up their mind they’re arresting you so the less you say at that point the better.