I have a long term bull, I've been seeing him for 13 years now. At this time I see him about twice a month. It's good for both of us as we know each others bodies better and I know what he like and what he expects me to do. Also since we have known him for so long my husband has no problem with me heading over to see him alone. I enjoy (and often don't notice) that my husband is there watching, but my lover enjoys having me to himself sometimes.
That said, he is in no way my only bull. I have a couple of other regular bulls, and I also enjoy trying out new guys occasionally. Each give me a different type of pleasure. My long term bull gives me a comfortable evening of non-stop sex, I know what to expect and what I will be getting. A new lover gives me anticipation and excitement, how big is his cock? how will he fuck me? what new things will he try with me?
I thoroughly enjoy all of my lovers, but for different reasons.