Is it forbidden to supplicate to Allah not to marry, and is that considered ill-mannered towards Allah, and what is the ruling on this supplication?

Marriage is desirable, and it may become obligatory due to a specific circumstance. It is a great benefit and a Prophetic Sunnah (definition). The problems within it are few compared to its benefits, and they are part of the nature of life. Supplicating for failure in marriage is blameworthy because it is a supplication for something Allah dislikes, and there is a fear that it may be an transgression in supplication. It is better to supplicate for success in what pleases Allah and for the facilitation of good, and to supplicate for a righteous spouse and to avoid marital problems, and to abandon this disliked supplication.