Gwen might be a bit thick but even she gets it eventually- she won't be that easy about it, though!
In my mind, that was why Ianto was quite reluctant to declare his relationship with Jack: people wuld make assumptions (probably based on his age compared to Jack's) about who was 'submissive' there...
And basically the man that Lisa has dumped has ended up with the man that Lisa has probably been fantasising about...
So pleased you enjoyed it!