Steve knows Tony loves him, even if Tony's never said it. Steve doesn't expect him to; Tony has scars from his childhood that have never healed that make Tony hesitant to give his trust and his heart. Even though they've been together for over a year, there are moments when Steve can sense Tony's fear of rejection, his fear that one day Steve will decide he's had enough of Tony's sarcasm and emotional problems and leave him. It's something Tony will never admit, and the only thing Steve can do is make sure Tony's fears never come true.
Almost dying can radically change your perception, and it wasn't long after the Loki debacle that he and Tony found themselves in bed, desperately kissing and touching and reassuring, high on their narrow victory. It could have destroyed their growing friendship, but Steve didn't blame adrenaline when they woke the next day tangled together as it would have been easy to do, and he didn’t let Tony run and hide, either.
Their relationship developed slowly, so slowly that Steve sometimes wondered if Tony would ever open up to him, but when they finally kissed again after a sparring match, it felt natural and comfortable, an inevitable outcome, a reaffirmation of what they felt months ago when they fell into bed. Any lingering doubts and walls melted away in the wake of that kiss, a kiss that cemented everything. The first time could have been a fluke, something borne of desperation and never discussed again. But a relationship would never have worked then, if they had rushed into it without taking the time to trust one another, and now that they did have that deep trust, Steve knew they could last.
After their ten-month anniversary, Tony started dropping hints about Steve moving in, though he never actually asked. It took a month of Tony hiding Steve's toothbrush and razor in the bathroom cabinet, mixing their clothes in his closet so that Steve couldn't easily take them home, and wanting to stay in every night and cook dinner together instead of going out for Steve to finally do the asking himself. Tony teased him about it in typical Tony fashion, but Steve just smiled, because he could taste the relief and happiness when Tony kissed him.
"So that's a yes?" Steve asked when their lips parted.
Tony only kissed him again and dragged Steve back to bed. It wasn’t until after, when they were finally satisfied hours later that Tony said, "That’s a yes."
Steve smiled and drew Tony close, whispering his love in Tony's ear, and even then, when Tony still didn't say I love you back, Steve wasn't hurt. He understood why Tony found saying those three words so difficult, but it didn't matter because the words were meaningless if they weren't filled with love. The love itself was what Steve wanted, not hollow words that felt like an obligation, and he had love, that he knew for certain.
Steve doesn't need to hear the words themselves, not when Tony already tells Steve I love you in different ways. Tony says I love you everyday with his lips when he gently cradles Steve's jaw and leans in for a lingering kiss. Everyday with his hands when Tony draws him close and trails his fingertips along Steve's spine. Every day with his eyes when Tony wakes him with tender kisses on his face and makes sure his face is the first thing Steve sees. Everyday with his body when Tony presses him into the bed, undressing them slowly, both of them warm under the sheets.
Tony shows him in so many ways just how deeply Tony loves him that Steve never felt something was lacking in their relationship, and so it actually came as a surprise when Tony did say I love you for the first time. It was so cozily domestic that Steve has to smile when he thinks about it.
It was late, and Steve was in the bathroom, brushing his teeth in his boxers when Tony came in, reading glasses perched on his nose and just in boxers, too. Steve glanced over at him and smiled around the toothbrush, and Tony came over, silent, and pressed against Steve's back, arms sliding around his waist.
Steve wasn't expecting it. There was no build up, no grand romantic gesture, just Tony's eyes locked on his in the mirror and Tony's lips brushing his ear as the words I love you were beautifully whispered and went straight to Steve's heart, warm and precious. It was perfect. Steve stared at Tony in the mirror, toothbrush hanging out of his mouth, forgotten, and Tony only smiled and held him tighter.
"I just wanted you to know," Tony said simply, and then he left, going back into the bedroom, after a sweet kiss on Steve's cheek.
Steve blinked a couple times, the full import of the words slowly registering in Steve's mind, and when they did, the smile couldn't be stopped. Steve quickly rinsed his mouth so he could join Tony in the bedroom, and he crawled over Tony, their faces so close they could feel each other's breath. "I love you, too," Steve said, and Tony's face was more open than Steve had ever seen, Tony finally convinced of the depth of Steve's love and letting Steve as fully in his heart as he was in Tony's. They kissed and touched, caressed and whispered, stripped each other bare in more than one way, and spent the night showing each other how deeply their love ran.
Things have been sweeter since then, as if the invisible wall that Steve kept trying fight was destroyed. Kisses and touches are more frequent, as are small, secretive smiles, shared when they can't kiss or touch. Tony still doesn’t say I love you very often, but Steve doesn't mind. He just enjoys when Tony does, smiling and murmuring the words in return. Every I love you that passes Tony's lips is a sweet gift that Steve holds close to his heart, filling up all the cold, empty spaces that Steve would always be there, Tony a companion that Steve can't imagine being without.
All Steve wants is to do the same for Tony, be the same, because Tony's been hurt too much, used and then abandoned. Steve wants to take that pain away, replace it with something lasting and good, and make Tony truly happy, not just superficially, the way Tony has made him. It's a formidable aspiration, one that won't be quick or easy to fulfill, but Steve's never shied away from hard work, especially hard work that means as much to him as this does. He's looking forward to spending years making Tony smile and laugh, his eyes crinkled at the corners, so that Tony forgets what it was like to feel unloved and alone. And each day when the lurking shadow in Tony's eyes from all his past hurts gets fainter and harder to detect, Steve believes a little more that maybe someday he will succeed, and Tony's pain will be nothing but a vague memory, eradicated by love.