In my opinion,Paulie was sucking up to New York for a very practical reason. In the event that Tony was out of the picture,Paulie was laying the groundwork to become the next Soprano Boss. He figured by pretending to be only interested in good relations between the Families, he would be seen as a guy who could step up and continue the status quo with the Lupertazzis, and that Carmine,(or Johnny,or little Carmine,or whoever) would want him in charge. I think the real situation would have been a surprise to Paulie. Once a snitch,always a snitch. No way would the Lupertazzi's trust someone who betrayed Tony in spite of their years of friendship.If he did it to Tony why wouldn't he do it to a Family he had no history with? And make no mistake,if Paulie was given the contract on Tony,with the promise that New York would back him as new Boss,he would have done it in a heartbeat. Of course New York would deny the arrangement,and Paulie would have been in the same boat as Tony Caponigro in Philly.
On the other point, I think Tony did love Paulie,but thought of him as a loudmouth and a gossip. He was like Tony's pit bull and certainly the toughest guy in the Family,but I don't think Tony would have hesitated for a second to whack him if he had to.