This is one of those silly "I voted for this, but I really think this" comments.

Re: monogamous, I think they've Had The Chat and they're currently effectively monogamous, but what's actually going on is that Jack has agreed not to look for other partners for the moment while Ianto tries to get more comfortable with the idea of poly. The whole "Gwen threesome nao? LOL!" bit in Adrift comes into this in ways I haven't quite worked out.

Hockey stick: pain play, see, 'cos of Jack's enhanced healing and I read this Buffy fic this one time that centred around the interaction of Slayer healing powers and BDSM and *cough*.