The Hidden Third Option: Don’t Play This Character
Based on information in the main text of the post, as well as answers to questions in the comments, this character:
- Has never been played at all,
- Was not accidental, but designed in full knowledge of the nature of the adventure you’re going on, and
- Lacks the typical warlock “easy out” by having the character an enthusiastic, actively loyal supported of Asmodeus
- Seems to lack enthusiasm and support of the GM
You’ve identified the major symptoms of the problem: You as a player face the stark choice of either playing the character true to itself and working against the party, possibly ruining their enjoyment; or remaining true to the group of players and characters but not remaining true to your own character.
This problem has a name, as others have mentioned in other answers, is My Guy Syndrome, named for the refrain most often heard with these characters: “But that’s what my guy would do!” where that is inevitably something detrimental or even opposed to the party’s general goals and well-being.
But the now-standard response to that is that the character only has those traits because you put them there.
Now, there are ways– in theory, with support from the right GM and often from the right group of players– that this sort of character can work. Other answers outline the general path to that, which involves a lot of coordination with the GM and possibly the players.
This isn’t that answer.
This is the answer that is very skeptical that you can square the circle inherent in your character, and get support from the GM and the players. It’s not impossible, but I am skeptical.
This is the answer that strongly encourages you to meditate on why you created a character that, by definition and if played straight, must be in conflict with the rest of the group, and to consider if the fun you have in playing this character will come directly at the expense of the fun of the rest of the table. (Mostly because your character’s goals and the party’s goals seem to be completely against each other.)
This is the answer that strongly encourages you to modify the character enough that it can be on board with the general goal of the campaign. Whether that means just changing the nature of the Warlock pact or scrapping the character and starting over is something no one can answer but you.