Clint had never experienced love. Of any kind. His parents pretty much neglected him. His brother betrayed him. The first time he felt love for someone was Natasha. It was platonic at first. He was proud of her. Slowly those feelings evolved. He held passionate feelings for her. Eventually he confessed and was accepted. They married soon afterwards.
For Natasha love was a childish notion. The Red Room had made sure of that. She didn't feel anything for anyone beyond friendship. But then Clint walked into her life. And Natasha found herself a slave of love. He saved her. And it almost took losing him to Loki to admit her feelings. They were now married. She was happy and contented.