what do you mean, your wife having a boyfriend on the side? Where there is more than just sex? I actually like the idea. My wife has had sex with about 8 guys over the past couple of years, but only a couple of repeats. I think a bf would work better for her. I know it sounds strange.
Personally I enjoy both categories.
Nothing like having a longer term bull for me. But also the thrill of a one night stand is attractive. Makes me feel slutty when a bull I don't know well pumps and dumps.