Jack Harkness and Ianto Jones
Jack trusted Ianto more than he trusted any other living being. There were some people high up on the list of people he trusted, but no one would be higher on the list than Ianto. He wouldn't do anything to Ianto to betray his husband's trust in him, either.
Which was a reason why he was always honest with the man. Whether it had to do with who he flirted with (or more) or anything else. He would not lie to Ianto.
"Churros are delicious," he said, as he followed the man toward the food vendors.