retro spoiler then: Gwen's been an absolute bitch to Rhys. She cheated on him. With Owen/ Then confessed it to Rhys. Only to slip him an amnesia pill (yes, of course Torchwood has those) straight after, so basically it was just to make herself feel better.

I don't think Jack is opposed to sharing someone's heart(s) perse, as long as he's in the group (9/Rose/Jacl OT3 for the WIN). I really like your idea of it being Jack who leaves the Doctor for his own good (cue Doctor angst of extreme).

And your scenario with Ianto sounds (sadly) more plausible than a complete 'happy-ever-after'. However, and you obviously didn't know this, Ianto's feelings for Jack are everything but clear. In an early episode it turned out that Ianto was hiding his half-human, half-cyberwoman girldfriend in the cellar, trying everything in his power to fix her and make her fully human again. Of course it all went wrong as she went on a killing rampage, resulting in lot of guns being pointed in all directions (Jack and Inato threatening to kill each other in turn) and Jack killing her in the end. So. ANGST. And darkness and bitter, broken Ianto, who is all smooth and polite on the surface but...

And once the reruns hit the screen you totally will watch the show. And there's always dvds...