They didn’t always share a bed. Hell, some nights Tony didn’t come to bed at all. She spent those nights in her own suite, sprawled across the blankets, cats heaped up over her feet. Presumably Loki did the same, though sans cats. She didn’t know.
Mostly, though, they did. All three of them, jumbled together in Tony’s huge bed. Tony in the centre, both to help him feel safe enough to sleep and so he couldn’t sneak away. Loki on the side towards the door, often on his back, one hand flung toward Tony. Summer on the other side, tucked up close to Tony.
Sex didn’t actually happen as often as some people might expect. They actually spent a lot of time simply piled across each other’s laps, talking softly, cuddling, petting.