Yup the chastity was a plot point. Though it's in incredibly frustrating one. A hidden term of contract between Keichii and Belldandy was that he would be forcibly purged of all sexual desires towards her. Because something bad happened similarly in the past. And she knew but didn't want to tell...
Oh I really don't like this. Almost as bad as Keichii situation from Ah my Goddess when he was divinely castrated and he was never told and the love interest knew and keep that information secret.