Would you kiss a guy in a relationship under these circumstances?

If there is this guy in the group you usually go out with that you like for sooo long but he is in a relationship, so you stay friends even though he sent alot of mixed signals. Then before you leave the country by a week he kisses you passionately, and he tells you to keep it your secret, would you kiss him again if he tried another time, or what you do instead??
PS: keep in mind that you have liked this guy for so long!