[spoilers] Lucas. Just Lucas.

[HellsBells]

But Lucas cared enough for Dimitri not to want to leave him on that ship in 9.1, and when he told Dimitri to 'go get a skin-full and start again in the morning' in 9.5 cleared showed he at least he felt for Dimitri and knew him well, although this wasn't shown on screen. There was clearly a gap of time between Ros's funeral, a few days after the bombing, to Lucas and Dimitri being on the container ship, time enough for them to get to know each other.
Lucas' relationship with Beth was never explored enough, clearly he didn't like her at first, but I think he changed his mind, otherwise why ask Harry to keep her on at the end of 9.2.