No better way to ruin friendships than playing poker drunk, winning big on your friends or losing the same, greed and envy really builds the base of friendship!
But the same goes for not betting games, they have ruined many friendships
That is why with friends should play only with low stakes.
If you lose a little, you're not that angry, and is mainly about fun.
But you're right, that gambling can very easily ruined friendships.