It's the touches that Ianto could never give up.
The gentle fingers stroking along his sides, his thighs, his cheek in a heated moment of frenzied passion.
The drumming of Jack's fingers on his knee in one of the Captain's rare moments of boredom.
The feel of his strong hands wrapping tightly round his back, the tension in his taught muscles slipping away.
The sensation of Jack massaging shampoo in to his scalp, his entire body pressed up against Ianto's back, as water slithered over their bodies in a steady stream. The Welshman is unable to do anything but shiver and whimper in such immense pleasure.
The scrape of nails against his back as he shamelessly moans under Jack, just on the verge of pain, but undoubtedly pleasurable when Jack pressed his lips to the red streaks as they recovered their breaths.
The kisses aren't bad either.
The chaste joining of lips in a rush as they wrestle with their clothes and clamber to the bedroom.
The slow, sensual kisses, when Jack really took his time to explore Ianto's mouth. His hands always stay at the nape of Ianto's neck during these kisses, because in all honesty Jack can't find a greater pleasure than physically feeling Ianto's hairs stand on end.
The messy ones are also enjoyable. The frantic clashing of lips, tongues, teeth, it's far from perfect, but at the same time that's what make them so impossibly flawless.
The rare tender ones, after a particularly tiring day, when all Ianto wants is to kiss and cuddle and show, never tell, Jack how much he really loves him. Jack reciprocates by the bucket load.
He also really loves the innuendo.
The way Jack makes him feel so at ease, so comfortable.
The ever varying nature of their conversations, from those laden with subtext and dirty jokes, to those moments of intimacy, basking in post-coital bliss, soaking up the cheesy pillow talk.
The fact that he can never tell when Jack is being completely serious or not. He's found that when it comes to innuendo, Captain Jack is being deadly serious 99.999% of the time.
The way that he knows he's never felt like this before, no matter how much he used to try to kid himself. The conversation had never flowed this easily, and the sex was never as exciting with Lisa.
And of course he would be lying if he didn't say he loved the sex.
When it's fast and furious, rhythmic thrusting and gasping as he's shoved mercilessly in to Jack's desk.
When it's dangerous and he gets that flutter of anticipation deep in his gut. Like those times Jack would insist on sex on the invisible lift. Ianto had never felt so thrilled, yet so horrifically scared in all his life, as he did that night, kneeling on the cold paving slab, and taking all of Jack in to his mouth.
When it's slow and Jack looks straight in his eyes. A declaration of love in the eye contact alone. And afterwards, when Jack just lays on top of him and holds him until they both fall asleep, he can't help but be overwhelmed that this glorious man would even dream of sharing his bed with an ordinary Welshman who has a police record for stealing a packet of chewing gum.
It's the simple things Ianto loves, but when Jack takes his hand in the middle of the Bay, twirls him around, as if to show him off to the world, shouting his love for the coffee connoisseur at the top of his lungs, Ianto can't help thinking that the over-the-top romantic gestures aren't too bad either.