Agree with this. Ianto does go to extreme behaviors in CW in his efforts to save Lisa, and while some of his behavior might conflate with an addict's behavior in satisfying their craving, and a compariosn might be useful to a certain extent in analyzing and understanding some of Ianto's behavior and the underlying dynamics of it, I think the comparison ultimately fails for me when it comes to the question of what is the "fix" Ianto is supposedly addicted to? He is in love with Lisa, he might be obsessed with saving her, but obsession and addicton are ultimately different things.

And yes, the episode is about love -- they've practically painted neon signs throughout the episode making it clear it's about love. Off the top of my head, Ianto asks Jack "haven't you ever loved anyone?" in addition to insisting numerous times he loves Lisa / is doing this because he loves Lisa; Lisa suggests she transplant her brain into Ianto's body, making them into one being, because "isn't that what love is?"; solitary_summer already mentioned the transplant into pizza girl's body; and in case anyone still didn't get it, Gwen asks Jack again, at the very end of the episode, "have you ever loved anyone that much?" At which point Jack throws a significant glance in Ianto's direction but doesn't answer Gwen's question. ;)