You need to beat him on the coin flips
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You have to talk about weapons in the morning with rune and tisthel, after that you choose the redder the better and you Will unlock a especial dialogue with him, once you get the chance talk with alon, you need to ask for his sexual life and you'll get the coin toss option.
I recomend save before the coin toss so you can be faster at the time of save and reload.