> The very fact that my truth is not your truth, means there is more than one truth, does it not?

Not necessarily...

A lot hangs on language.
I could say 'I have no friends'.
Once it has been clarified what is meant by 'friends'
Once it has been clarified who the 'I' refers to
Once it has been clarified precisely *when* is meant

then the statement is either true or false
(regardless of whether we believe it to be true or false there is a fact of the matter that lies beyond what we believe to be the case)

> Even "scientific" truth has been known to be adjusted from time to time.

I would describe that situation as follows: Sometimes scientists think they have discovered a truth but over time... turns out they were wrong. They didn't discover a truth at all. in fact... they believed something that was false. happens all the time ;-)

in philosophy we distinguish between two different fields of study / two different topics / issues:

metaphysics - what actually exists
epistemology - what (if anything) we can know about it.

the only things that can be 'true' or 'false' are utterances (language) and thoughts.

So there may be some truths that we will never know (for example 'phi is infinite' is either true or false regardless of whether we ever manage to construct a proof of that or not)

> It's a very difficult thing, for some, to realize that just because there are different "truths" does not mean that nothing is stable. The approach does not shake your very foundation of beliefs, imo.

depends on how thoroughgoing the relativism is...

most theories... deal with 'relativism' on the level of semantic (meaning / reference) ambiguity.

so once the application / reference / meaning of the statement is clarified...

it is either true or false