I think this is right. He definitely fancied Dani at one time, and thought she was wasting herself on David, even before it was revealed that David was gay. Jac always had an enmity towards David, and it was mutual. Remember the fight that landed Jac in hospital.
I thought when we'd seen Jac's place before, it looked quite nice, and it had a great sea (or estuary) view, although I suppose there are a lot of those in the area.
I couldn't quite understand Jac's reluctance to move in with Llio. I wondered if he had some secret love interest that we didn't know about, and wanted to pursue it away from the prying eyes of friends and colleagues.
I have a feeling that Jac and Dani will end up together one day. Although I suppose Jac and Llio getting together is a possibility - Jac will certainly be more fun the the Bio(?) lady. (or was she a Geography teacher ... no no let's not be cruel to Geography teachers! ).
I'm pretty sure that Lowri fancies Jac actually, but I don't think she'll do anything about it (well not unless the scriptwriters become really desperate for a story-line...).
BTW, in the programme website list of characters, we are told that Jac is a "love em and leave em" type of character. We haven't actually seen much evidence of that, to be honest.