As I explained with sources here, a maxim that is used as input for the categorical imperative does at the very least contain
- a particular situation
- a particular intent that the action seeks to achieve and
- the particular means/action to achieve that outcome
Therefore, very general principles like "live unmarried" are not maxims proper.
Throughout the history of philosophy, many such examples were used to try to ridicule Kant, like that it would mean using the tennis court around the corner on Saturdays at 10:00 in order to play with friends when it is quiet would be immoral since when everybody would do it that obviously defeats the original intent. Thus, we see that neither too generic nor too specific input does work well. And in fact, Kant's own examples of maxims show that a specific intent doesn't make a maxim since a maxim should be "the subjective principle of the action" (4:420 fn. 2), ie. a rule governing the choice of action, not simply the chosen action and intent itself.
Taking the tennis-court example, the proper maxim would be "If I want to play relaxed rounds of tennis with my friends, I should choose a time and place where the court is quiet." et voilà, no contradiction whatsoever.
Therefore, applying the categorical imperative cannot mean generalizing one's own decision but is about generalizing the particular principle that made you choose this action over another one given your particular situation, needs, and options.
That is why Timmermann discusses the above-mentioned aspects of a maxim since you basically have to judge your process of deciding for a particular action by generalizing. This process has to involve careful, rational consideration of what you actually want, the context (situation), and other possible courses of action.
Understood this way, we see that there is no (moral) harm done in living in celibate if the decision is reached in rational consideration of the particularity of one's own situation, other possible ways of life, and the needs and interests of other rational agents. Mind, living in celibate is not a particular action in the first place though, it is rather a continuous lifestyle following a more general principle.