Mathematical truths are absolute truths, for example, "square root of 2 cant be obtained by dividing 2 natural numbers" that is an absolute truth.

I guess apart from math truths, and the fact that you exist there arent other absolute truths. but there are other truths that even if not absolute, the evidence supporting them is overwhelming.

"why should I have any faith in what I believe?" You shouldn't have faith, you should just follow the evidence wherever it leads, and you should be aware of the evidence that is supporting the things you think are true.

"Haven't you had moments where you thought you knew something but it turned out later to be false?" happens to all of us, one very common is realizing the religion we were indoctrinated into is false, or realizing many political or historical assumptions that many people holds are wrong, also we get dissapointed from some people, all of that is totally normal.