Things do tend to get complicated between them, and that's a part of what's made him so hesitant, knowing how much simpler things have been for Ianto with just Spike and how much more complicated they are now he's back in the picture again. In relationships gone by he probably wouldn't even have worried about it, just gone barging back in without a second thought, but Ianto and Spike (as well as other people back at MarinaNova) have massively deepened his understanding of how others are affected by such things and he is at least a little more sensitive now.

So he's aware that things are still a little off between them, but like Ianto he's happy to ignore that for the moment in the face of the comfort Ianto's offering right now. As Ianto begins to open up more to him, he lets out a little moan and lunges into the kiss, heat and need and more specific want for Ianto, as he begins to let himself realise just how much he's missed him.