About trusting our Guardian,
as far as I'm concerned there is very little that links the guardian to the artifact beyond his dubious claims, dubious because they are on the face of it misleading, purposely obfuscate who he is, his situation, and by extenstion is role in our predicatment. His only tactic to persuade us is a clumsy appeal to our emotional understanding, and whenever we question him on more substantive grounds...oh no they're attacking again farewelllllll! *I will always love you* *remember me when I'm gone*
Based on your postings it is clear you don't trust and don't like him personally and that is ok. No reasons required if you feel that way.
But - he is shown to help and protect us, we do show symptoms for turning into a mind flayer and he stops it. And he saved us from the fall - if you think he is lying - who do you think saved us? The Absolute and her followers want us dead (as seen if you meet the deadly injured guy and his siblings). And we see before the goblin camp that it is the artifact that protects the group. This is a link from the artifact to the dream guardian. And later we get more connections (like him warning us, you hear the dream guardians voice and then he moves the artifact back to you -> but this is e.g. in the monastery / creche so basically act 2).
And yes, he is hiding behind his appearance and it is especially clear if you have a male guardian and talk to gale, who speaks about a female one. So there is some hiding / deception on his part (which is later explained why he did it - because people normally don't trust mind flayers).
But what he tells you is true (e.g. he tells you he wants to be free. That is true. Also some things more like from past view - he was an adventurer, he had a tadpole in his head...). He isn't really lying, more lying by omission and not telling everything, which again, is understandable.
And he is in parallel protecting the player character + group and fighting off the honor guard and then talking to you (and your companions - at least in the beginning) - so everything at the same time. I think it is understandable that he won't have a lot of time for a chat and he doesn't want to tell you everything because he needs you to trust him first - and to be able to trust YOU. He was stabbed in the back by his former lover (Ansur tried to "mercy" kill him while he was asleep). He needs allies, he can't do it alone. He uses his natural abilities to achieve his goal - and this goal alignes with the players (in a good ending at least).
I also think people are very harsh to him for things that our companions do as well - like Astarion - he is manipulative too. He tries to manipulate to make you his ally, just like dream guardian/Emperor does. He also tries to hide what he is at first - out of good reasons too.
In the end, we see we can trust the Emperor and even if we used tadpoles / astral tadpole it is reversed in the end. No harm done.
