I also thought the ethics of this show were highly dubious, especially for a mid 90s BBC1 Sunday night (IIRC) family shitcom.
Not only does a married man 'have it away' but he keeps it up, marries her, and
gets her pregnant. The whole time COMPLETELY lying his arse off to everybody, except his 90s mate.
As for the whole "oh its in the past so that's ok" well I'd like to see most people's reaction to finding out their husband or wife had been having an ongoing illicit affair behind their backs, I don't think they'd be that happy about it, time portal or no time portal.
... I know it was only a sitcom but I'm just saying