I'm not sure I understand everything in this passage...but it would seem that Paul is explaining why he made a promise to visit the Corinthians...and then later went back on that promise ("in order to spare you that I did not return").

Even Paul had times where he didn't keep a promise. Only God can make promises that will never go out null and void; He has (and will continue) to keep every promise, no matter how small, made to us. Thank you, God, for your total faithfulness.

2 Corinthians 1:15-24