Jack's not into morning-after chats, but in the aftermath of hard, sweaty sex he sees that Alonso needs to talk.
Jack remembers the spaceship that narrowly missed London. Now he learns the details. Innocent lives sacrificed to greed. The Doctor's desperate journey. Alonso's nightmare on the bridge, wounded and alone.
"They called me a hero... but I got sacked. Nobody wants to hire a 'hero' from a jinxed ship."
After Alonso falls asleep in his arms, Jack finally understands the Doctor's gift. Not an opportunity for a casual shag - instead, a chance to help another wounded soul find healing.