It is not uncommon for a Player Character to hide secrets from their companions, be it their past misdeeds or their burning love for an antagonist.
While it's perfectly fine for characters to have secrets, Players should instead keep things transparent and work together to get the most out of the situation.
By telling your group "My character looks like they want to be friends with you, but she actually hates you because of what happened in Galatea" you are empowering everyone at the table, including yourself: now that this facet of your hero is known, it will be possible to build upon it and create drama.
Never forget that this game relies on a collaborative storytelling effort: disclosing your character's secrets means giving your fellow Players a chance to make things interesting — do not think of it as "letting your guard down".
There might come a moment when you feel like your character has been fully explored; they have faced their fears, achieved their goals, and found who or what they were looking for, with the campaign not yet reaching its end.
When this happens, you are free to announce that your character will be leaving the group — you should do so between sessions and also come up with a replacement character. Then, at the beginning of the following session, describe your character's epilogue and agree on how and why your new character joins the group.
Needless to say, you can only switch to a different character if that character is somewhere nearby or has the means to reach the rest of the group.