Secrets
You keep secrets from each other because you can't bring yourself to be honest. And it applies when you keep things from yourself too.
Harry keeps things from Peter who keeps things from Mary Jane who keeps things from Harry who keeps things from Mary Jane who keeps things from Peter who keeps things from Harry.
Harry convinces himself that Peter doesn't know that Mary Jane comes up to the house and to his bed most nights. Peter convinces himself that Harry doesn't know that Mary Jane climbs into his bed afterwards, still smelling of Harry's cologne with his come slick on her thighs. Mary Jane convinces herself that both Harry and Peter don't know what she does after she sleeps with both of them.
And they all convince themselves they don't like it. Harry doesn't like it that he was first, Peter doesn't like the taste of Harry on Mary Jane, Mary Jane doesn't like being fucked twice in one night.
They spent one night after Harry's father died, Peter and Mary Jane held into place by guilt and grief, all three curled up on the big masculine leather couches that were now Harry's. Harry was drinking his father's scotch and Peter just kept staring at his roughened blistered fingers and Mary Jane bit her lip, trying to think of what to say.
When the faintest hint of sunrise peeked in from the penthouse windows, they carried Harry to his bed, Peter on one side and Mary Jane on the other, holding him close as they walked through the mausoleum that was once his house. He sleepily stumbled to his bed and then, before any of them knew what was happening, pulled Peter in for a slow and soft kiss.
Peter pulled back, looking at his best friend closely, then quickly looked at Mary Jane, his eyes wide.
She had the faintest smile on her lips, and bent down to kiss Harry on his forehead, laying him down onto the bed. She sat on the bed next to him, stroking his hair, and gestured for Peter to join them.
Peter was stiff and uncertain, but, after a few minutes of Mary Jane gently stroking Harry's hair and Peter's leg, he curled up next to her, nuzzling her neck, smelling the faint scent of expensive perfume and discount soap that made up the mystery of Mary Jane.
Harry pulled them both down against him, and, together, the three of them curled up on the bed, each trapped in their own private secret grief but trying to hide the pain. The complex pleasure of touch, of sound, of sensation. Harry's hands on Mary Jane's thighs, Peter's arms wrapped around her waist, lips against lips against lips against hips against fingers against breasts against back against skin against akin against skin.
They finally fell asleep as the grandfather clock struck noon, a tangle of limbs and softness, Mary Jane's red hair trailing over all three of them.
It was the one secret they shared together, the one thing they never spoke of again. Mary Jane takes the elevator to Harry's house in the evening and takes the subway to Peter's apartment at night. Harry buys her fine silk dresses and waits for her to return creased and stained. Peter tells her of the people he saved and calls her a whore as he comes.
You keep secrets from each other because you can't bring yourself to be honest. Even superheroes have that problem. And keeping things from yourself is the biggest problem of them all.