Was the Tet offensive the main factor for the end of the Vietnam war?I am aware that it is a factor but im am not sure if it was the deciding...

You could definitely argue that it was, but there is no
one correct answer as to what the main factor in ending the
war was.

The war ended because Richard Nixon felt that the
US had to get out of the war.  He saw how unpopular the war was and decided the war
needed to end.  He promised "peace with honor" and got the US out of Vietnam in 1973,
five years after the Tet Offensive.

Nixon won the election
of 1968 in part because Lyndon Johnson dropped out of the race.  Johnson dropped out
largely because of public outcry over the war after the Tet Offensive.  The public had
been led to believe the war was practically over and then Tet showed that was not
true.

In this way, you can say Tet led to Johnson dropping
out, which led to Nixon winning.  Nixon's win led to US withdrawal.  By saying this, you
can argue that Tet was the main factor.