If you don't mind me asking, where did you read that he took a vow of celibacy? There's actually considerable debate around whether Æthelstan's apparent lack of a sex life was a conscious effort, or just a thing that... happened. Foot's recent work on Æthelstan indeed suggests that he may have avoided finding a wife and having children while his own succession was in the balance, and that post-coronation, he found himself too busy, or simply so surrounded by eligible heirs that he just didn't bother. Æthelstan's reign was the context for the gradual healing of deep political rifts, and any suitable marriage is likely to have been deeply contentious to at least one faction. That said, we actually know remarkably little about Æthelstan as a person - he has no contemporary biography like his grandfather - and it's entirely possible, if admittedly unlikely, that he had a string of lovers and illegitimate children. We do know, however, that he was a capable battlefield leader and, as well as collecting relics and taking an explicit interest in criminal law, he enjoyed the stereotypical contemporary male pursuits of hunting, riding, poetry, and gambling.

It's worth noting that Æthelstan was king of the Mercians for some months before his eventual accession to the throne of England and, despite his West Saxon heritage, did struggle to gain the support of the Wessex nobility early in his reign there. His coronation was actually unusual though. He was the first king to forgo the typical English coronation, in which the king is 'crowned' with a helmet, and instead adopted the continental fashion of an actual crown accompanied by the symbols of office; an orb, sceptre, sword etc.