The state of being single is what we’re all born into and remains the situation for those who have not found a vocation to marriage, priesthood or religious life. Could it really be a choice? It is a vocational choice provided it is chosen. It is commonly from within the single state that we discover the first dimension of our vocation, our call to holiness as a baptised person. The other dimensions are my state of life and my work. The natural desire to marry and have a family leads most Christians to marriage as their chosen state of life. But marriage is only confirmed as your vocation when you meet your spouse and exchange your vows. Similarly, the vocation to the priesthood or religious life is confirmed by a bishop ordaining you or a superior receiving your vows. So for these three states of life there is external confirmation by the Church that this is your vocation.
If none of these three vocations is confirmed in somebody’s life, they then have a choice: to remain open to one of these three states of life at a later date or to embrace the single life as a permanent, stable part of their vocation. To the person making the choice to be permanently single as a lay person, the Church can offer support. This support might come through a decision to seek deeper involvement in the life of the local church community; some lay people in the single state lead lives of outstanding service to their local community. To embrace the single life as a lay person in a lifelong commitment is sometimes called apostolic celibacy.
Although there is not a formal confirmation process as for other vocations, this is a real vocation and is of increasing significance in the life of the Church.
(Website of the National Office of Vocations UK)