Bruce Banner never thought he would find love again. Who would love a monster. But he was proven wrong when the Avengers were formed.
He met Clint Barton. Clint who was as broken as he was. Clint who believed he was the true monster because a maniac God forcee him to kill his comtades.
Bruce naturally seemed to gravitate towards Clint. He thought it was because the archer had an easy going attitude but it was because Clint was afraid to lose contol just as much as Bruce was.
They started a tentative friendship and slowly they became close friends to the point that Hulk got involved.
Bruce didn't know when but he had fallen in love with Clint. His feelings were deeper than his feelings for Betty. Clints easy attitude, his understanding of both Bruce and the Hulk and the fact thst he made Bruce feel comfortable in his skin and not like the time bomb he was.
Clint was also the one who told him that his alter ego felt more than anger, that behind the rage monster lied a gentle creature who just wanted to be accepted.
Bruce was afraid to pursue these feelings, but a little push from Tony and another close call on a Shield mission was enough for Bruce to confess to Clint. He was delighted when the archer returned his feelings saying no one completed him like both Bruce and the Hulk.
As Bruce watched Clint sleep, silently running his hands through Clint's hair, Bruce and the Hulk vowed to always protect him.