Cloud never stays for long; only ever around when he's absolutely needed, convincing everyone that he'd just be in their way and referencing the vague allusion to bad things happening to anyone he gets close to. But Leon knows it's having too little trust in himself to be around anyone; so wrapped up in past guilt that he unconsciously shies away from all human contact.
So Leon makes it a point to convey just how much Cloud is needed. Trying to subtly keep him ever closer, even if it's only to glance at him from far away; just knowing he's there is enough.
Cloud never starts anything, and even then his touches are always soft and hesitant, as if he's scared Leon will break under his ministrations. Leon knows it has to do with his past, something to do with not being able to control his own strength, something to do with chemicals and scientific experiments, something about a super human; but he doesn't know for sure because he's never asked. He knows better than to pry.
Leon knows not to ask unnecessary questions and let Cloud open up at his own pace; to let him be too gentle while he gets comfortable with the new experience.
It's usually Leon who instigates anything, with the blond's silent permission of course(because Cloud would never learn to trust him if he forced things on him). But there are those rare times when Cloud forgets himself and Leon can see a small flicker of what the warrior used to be.
He's never in his right mind. It is always after battle, when Cloud's skin is flushed and his breath coming in ragged pants. His nerves excited by the rush of adrenaline and his overly bright blue eyes are burning with lust and mako. He forgets he's supposed to be timid and stoic, pent up emotion flooding out as he moves toward his…(what are they exactly?).
He'll roughly press his bruised lips against Leon's and take control, giving little thought to his strength. It is only after battle, when his veins are humming with electricity and poison, that Cloud allows himself to come to life, allowed to really live and react like a human being.
It is almost always after moments like these, never any other time —moments had in brief lapses of reason— that they both surrender to physical needs and feeling.
Never at the house, because that's almost like tainting sanctuary, and it's much too familiar to stay adequately detached.
And Cloud never ultimately takes control, convinced that he'll break Leon. That he'll forget himself for a moment and have his only contentment taken away.
Leon doesn't always believe Cloud's insecurities, but follows the blond's rules anyways, knowing that going at this slow pace with all the conditions is the only way to get him to open up.