I actually don't think Ianto was jealous of Gwen (and I don't think he had reason to, either). It doesn't feel like it's about romantic feelings at all between Jack and Gwen.

But I quite like your interpretation! I especially like your Owen and his "He's a wanker, Ianto. You deserve better." It's really very much in character with the current depiction of Owen.

And Jack really does look and act like he is close to a nervous breakdown in this episode...

Great little ficlet!