why asking gav to join the trip?

[spoiler]Why is it that Deano tells Nige to ask Gav to join them? Wasn't Deano hating Gav's guts since the very beginning? Gav didn't even have a clue about the dead Norwegian, and it's not until the second night into the trip that Deano decides he is going to kill him on the lighthouse. What was then his reason to invite him?
I'm sure I'm missing something, please help me out![spoiler]



BTW, this movie was something else, I still have to make my mind about it, but it was thoroughly entertaining and gripping. The whole subject, and mostly the end, reminded me of Trainspotting, same kind of bittersweet ending... Like life itself.