One
From the moment they met it took roughly five hours for Jesse to realise that he loved Susan, he loved her laugh, he loved her strength, and he loved the passion she had for nursing. It took roughly 3 weeks for him to pluck up the courage to ask her on a date. They talked for ten hours, staying at the restaurant until closing time, and then sitting on a park bench. It took five months for Jesse to realise that although he loved her, she wasn't the one he was in love with, by then it was too late.
Two
He had never been the best father, but he had loved his son. He had thought that leaving him would be the hardest thing he ever had to do, but coming back was even harder. Seeing the man that his little boy had grown up to be, the successful doctor, partner and manager of a restaurant. The worst part was seeing him with the Sloan's was the worst part. Knowing that they had given him what his own father hadn't, love, warmth, safety. And he knew that he had lost his son forever, and it was his own fault.
Three
Being a detective, he noticed a lot, the little details that often gave a person away. Sometimes the talent was a blessing, often it was a curse. He noticed that when he made a dirty joke, Jesse went red. He noticed that whenever he got a date, Jesse became moody. He noticed that when Amanda made jokes about the two business partners being like an old married couple Jesse got a wistful look in his eye. In all his years as a detective, he had never ignored the evidence, which is why he was on the beach, holding his Jesse.
Four
Her relationship with Jesse had never been easy; there had been too much competition, off the other nurses, off the young female patients, off Steve Sloan. Jesse, of course, was oblivious to the love that the detective felt for him, but she knew. She had seen Steve's face when he returned and found Jesse safe in the bombed hospital; she had seen the jealous looks cast her way when he thought she wasn't looking. She knew that she had to leave, for herself, and for Jesse's sake. Because, even if the doctor hadn't realised it yet, he loved Steve too.
