Jack is defined by the people he has loved.
Jack had lived a long time and loved alot and fucked even more. It was a part of who he was, Jack the flirt, the romantic, the sex addict and he had lots of stories to illustrate his past. The mistake people made was to assume his stories fitted into his apparent 35 year lifespan rather than spread across his actual 150 years of living. Of course that would make it look like he was fucking like a bunny every night. When did his team think he actually found the time for that? He lived on-site and took the night watch for rift alerts, he couldn't go out for long or too far, he couldn't bring anyone back or stay over with someone else.
Before he had become the leader he'd had office romances, several in fact, this job tended to drive people together. Then if a relationship went sour he could disappear on a field trip for a while until things settled down but now he didn't have that luxury. So ever since total responsibility for Torchwood 3 had fallen on his shoulders on that eventful New Years Eve, he had been restricted to the occasional quick fumble in a dark alley when the pressure got too great, to satisfy, if barely, his physical needs. However his emotional needs, his need for intellectual stimulation, for physical intimacy outside of sex, his need for simple social interaction, he had got all that from his team. Jack prided himself that he was free with his affections and he had loved his team and told almost all of them that on a regular basis.
Tosh: Ever since he had rescued her from the Unit prison cell she had offered him her total loyalty and he'd offered her his protection, until the day that protection failed her. If he was to sum up their relationship in one word it would be "gentle". He had still flirted but only gently with Tosh, just enough for her cheeks to tinge with pink in embarrassment. He made sure to tell her often how brilliant she was and he loved the way it made her eyes glow. They had rarely talked on a one to one basis in the first couple of years of their relationship, but later when she had started to come out of her shell it was Tosh who would come to his office to gently chide him when he had slipped up and put him back on the right path. It was Tosh who could make him see where he had gone wrong. He had loved Tosh, he had loved her like a little sister.
Owen: Spiky, snarky Owen who had been hurt at Katie's loss and who had never fully recovered from that. Owen was a flawed man, he showed no respect for anyone and had a nasty habit of needing to find someone to blame. Owen blamed Jack for Katie's death because there was an alien in her brain and Jack was an alien hunter, he blamed Jack for Diane's desertion because Jack hadn't stopped her flying away, he blamed Jack for leaving them when the doctor came for him and he blamed Jack for bringing him back to the living death his life became, but in that case he was right. Despite those flaws Owen still cared, that's why he hurt so much when he lost first Katie, then Diane and why he died a second time, sacrificing himself for everyone else. As much as Owen was rude and selfish he was also incredibly brave and caring and Jack loved him. Jack loved him despite, or more accurately, because of his flaws because it is the flaws that maketh the man.
Suzie: She had been with him the longest, was his second in command but he'd known her the least. She had been a strong, intelligent, feisty woman. She had not been scared of Jack nor attracted to him. She had treated him with polite respect and offered her support as required. She hadn't poked or pried into areas he wanted to hide and he had respected her for that. She had caused him the least worry, the least problems, that is until she shot him in the head. He was confused about his feelings for Suzie, he loved her in a hands off fashion but mostly he felt guilt for not knowing her better.
Gwen: Loud and opinionated and big hearted. She gazed at him with these big, beautiful eyes like he was a sex-god. She challenged him and his decisions constantly and it made him feel alive. If it had been before and not after, he probably would have taken her to his bed. She reminded him alot of Lucia, not in looks but in personality and it would have been glorious and passionate and loud just as it had been with Lucia. It would also have crashed and burned just as it did with Lucia, because he would never have been able to live up to her expectations of him, never be the man she wanted. He would have got frustrated that she couldn't see all that he was, couldn't really see below the glossy veneer to the murky depths below and still love him. He loved her though, loved her for what could have been and it had hurt badly when she had married Rhys even though that was what he wanted for her too.
Ianto: There had been something about Ianto from the start. Despite the casual clothes and the young face there had been something in the eyes that spoke of experience beyond his years and deep pain. After the incident with Lisa when Jack should have booted the boy out retconned back to infancy, he had instead offered him mercy and his own bed.
Jack was not sure what prompted him to break his own rule, perhaps it was the fact that Ianto recognised that Jack could be a monster and called him on it. That the boy was pleasant to look at didn't hurt and behind his calm, quiet mask Ianto hid a fiery, passionate nature that Jack loved to provoke. Ianto would be the perfect, obedient assistant in public but would berate and discipline him, or sometimes, if it was required, comfort him in private. The fact that only he got to see that side of Ianto was a key attraction. Sometimes, though, they would just share a coffee and talk quietly about nothing, neither man was willing to give away too much personal information but both seeming to find comfort in the company. At those times Jack felt he could drop his high adrenaline, hero persona and just act like a normal man. It was ironic that Ianto was the one person he had never said "I love you" and the one person where he meant it in every sense.