Q. My partner and I have played tennis for many years. We are at similar levels and I enjoy playing tennis with him. He is a good player, but for some reason (maybe I make fewer unforced errors), I can win most of the games when we play. I don't want to lose my partner, should I lose some games on purpose so that he will not lose interest in playing?
A. Losing on purpose would be disrespectful to your opponent. If you are sincere, then you owe him your best effort.
You might, however, work on weaker areas of your game against him. The situation that you describe is actually ideal for this. For example, if you are a strong baseliner, force yourself to play like a net-rusher (by serving-and-volleying and otherwise looking for opportunities to get forward). The fact that you are doing this with a buddy against whom you usually win will likely allow you to develop confidence more quickly.