Sasuke's body is marred by brother-love. Every muscle, every fold and cress has already been touched and burnt by the hands of a dark lover, secretly cooing over the loveliness that is flesh and blood. Everything, from the soft cheeks that Ino loves to nuzzle to the creamy thighs hidden beneath tight cloth, has already been fondled and caressed in days innumerable and past. She is, in effect, dealing with used goods.
The others had trouble handling him, could not cope with the reality of someone who's lost their most beloved thing. Naruto grew frustrated at the failure of his efforts to piece Sasuke back together, to the familiar shape of friend and rival. Sakura became daunted by the ghost that hangs over Sasuke's head, the shadow that darkens his eyes. Kakashi tried the hardest, and so failed the most miserably, seeing in his erstwhile pupil his nightly thoughts made manifest in day.
Ino succeeds because she wants nothing from him, not even his love. It is enough that he lets her love him, lets her ardor envelop him like a flame. From the moment she first spied him, there has always been the constant desire to hold that sad face in her hands and kiss it till he relaxed in her arms. He stays with her now because he's unused to the affection she so unceasingly offers, to the hugs that once so chafed him and now are an immersion in warmth.
She knows he appreciates it, even if he can't say it. He is accustomed to heat of a different kind, more hard and fierce. It shows when he begins blushing heavily as she feeds him a piece of tomato, or when she insists they share a drink with two straws and he acquiesces, though still deeply scarlet. Expressions like this make her happy in a deep, unspeakable way. She thinks nothing of pursuing this shy boy with child's eyes.
Lovemaking is perhaps the most difficult of their occupations. He could not bear to be touched in the first few months, and even now she knows he would rather have the love of kin, the exquisite touches of painful eyes. But he allows her to hold him now, probably more out of guilt then anything else, and Ino will not lie to say they do not find it enjoyable, as she never fails to feel pleasure when kneading the armour that is his body, and because Sasuke will always come profusely at her hands.
It's a strange existence to be sure, loving a man who loves someone as much as you love him. It's a difficult living, contending with moonlight for a small scrap of a heart that can't bear much more bleeding. But territory has nonetheless been won, she is certain of this. He loves the flowers she brings him, and enjoys kissing the long tresses of her hair. But what ultimately keeps Ino going is the beautiful way he melts whenever she says "I love you", for it's his way of saying "I need you too." She is content to remain his air, the barrier between dark sea and bright sky.