I get the feeling from that first meeting that Bonasera had always kept his distance from the Don, despite the friendship between their wives. He considered himself an honest citizen & probably just didn't want to get mixed up with a mob family. His daughter being attacked & beaten was one of the few things that would've prompted his request for 'justice' from Don Corleone. Even then, his reluctance was evident because he dreaded the thought of one day (and that day may never come) being asked to return the favor.

Maybe that's why he looks so uncomfortable at the wedding.

Apple