We don’t know that Paul was never married.
This was St. Paul’s advice to the Corinthians (excerpts)
7 I wish that all of you were as I am. But each of you has your own gift from God; one has this gift, another has that.
8 Now to the unmarried and the widows I say: It is good for them to stay unmarried, as I do. 9 But if they cannot control themselves, they should marry, for it is better to marry than to burn with passion.
10 To the married I give this command (not I, but the Lord): A wife must not separate from her husband. 11 But if she does, she must remain unmarried or else be reconciled to her husband. And a husband must not divorce his wife.
Concerning the Unmarried
25 Now about virgins: I have no command from the Lord, but I give a judgment as one who by the Lord’s mercy is trustworthy. 26 Because of the present crisis, I think that it is good for a man to remain as he is. 27 Are you pledged to a woman? Do not seek to be released. Are you free from such a commitment? Do not look for a wife. 28 But if you do marry, you have not sinned; and if a virgin marries, she has not sinned. But those who marry will face many troubles in this life, and I want to spare you this.
29 What I mean, brothers and sisters, is that the time is short. From now on those who have wives should live as if they do not; 30 those who mourn, as if they did not; those who are happy, as if they were not; those who buy something, as if it were not theirs to keep; 31 those who use the things of the world, as if not engrossed in them. For this world in its present form is passing away.
32 I would like you to be free from concern. An unmarried man is concerned about the Lord’s affairs—how he can please the Lord. 33 But a married man is concerned about the affairs of this world—how he can please his wife— 34 and his interests are divided. An unmarried woman or virgin is concerned about the Lord’s affairs: Her aim is to be devoted to the Lord in both body and spirit. But a married woman is concerned about the affairs of this world—how she can please her husband. 35 I am saying this for your own good, not to restrict you, but that you may live in a right way in undivided devotion to the Lord.
39 A woman is bound to her husband as long as he lives. But if her husband dies, she is free to marry anyone she wishes, but he must belong to the Lord.
40 In my judgment, she is happier if she stays as she is—and I think that I too have the Spirit of God.
But we do know that Peter WAS.