Well I've listened carefully to the original conversation and I certainly didn't think anything Dexter said referred to homosexual sex, metaphorically or otherwise.
And I'm pretty impartial because I'm not liking either of them.
Callum is trying to paint Dexter in the worst possible light. He's manipulative. Dexter winds him up but why doesn't he just ignore him and stop having deep conversations with him? I've noticed that during these convos's Callum often twists Dexters words to try and unsettle him but it doesn't work. The man is a mess, so intense and unstable, and I really think they need to keep a close eye on him before he implodes.