He fell in love with Pepper a couple of years after he hired her. He hadn't known it back then, it was a new feeling to him, not unlike the feelings he had for his mother but with an edge to it. The desire was well known, but the other feelings he hadn't realised what they were until later.
Until after Iron Man.
He never wanted Pepper to fall in love with him. Even though they spent everyday together, even though their lives were intertwined so that separation would kill him.
He didn't think he was really the sort of man any woman should fall in love with. Or any man, he wasn't one to discriminate but that wasn't the point. The point was Pepper was in love with him, he could tell, and he didn't want her to be.
There were so many reasons why.
He couldn't commit to a woman, had never in the past. He could only really commit to his technology, his projects, whether they be weapons or cars. He'd had trouble committing to his own mother at times, often choosing his school work over her, his friends, his father.
Relationships involved responsibility too and that was a new concept to him, and before Iron Man it was an abstract idea. Pepper wasn't the flighty kind of person he was, she stuck by people, by him. She'd had relationships, a couple of boyfriends while in his employ, and they had ended mostly because of his demands, not because of anything Pepper did.
She would probably marry him if he asked.
He probably wouldn't have even considered asking before Iron Man.
He couldn't guarantee he wouldn't break her heart, and he didn't want to break her heart. He did love her after all. He was a man of few guarantees, few promises, little love.
When he told her this, while they were sitting in his lounge, Pepper sitting on his sofa, he pacing before her, she had simply laughed.
The joke was lost on him for a few minutes while she composed herself and got to her feet, then she kissed him. Hands running into his hair, body close to his, a smile still on her lips.
"What?" he asked.
She took a step back.
"You're an idiot."
"I'll hurt you," he told her.
"I'll take the chance."
"I'll ignore you, choose Iron Man over you," he tried.
"You already do that now."
He was running out of arguments, he didn't know what to do when Pepper was quick to answer him like this, she was good at arguing with him.
"Don't you want to be with me now?" she asked.
"Do you?" he asked. "You didn't before."
"You didn't love me before."
She kissed him again and he smiled.
"I do want to be with you," he said. "I don't want to hurt you."
"I'm not asking for promises Tony."
"I don't have any."
"And I think you have a low opinion of what you have to offer me."
"I have twenty years of sexual experience and a multi-billion corporation."
"I meant emotionally," she said, raising an eyebrow.
She wrapped her arms around him, pulling him close, smiling.
"So now what?" he asked.
"I don't know Tony."
"I don't," he paused, "I don't know what to do Pepper."
"Don't worry," she said with a smile. "I do."