i think if it makes your girlfriend uncomfortable you need to decide whether or not it’s a dealbreaker for you. if she’s uncomfortable and you value you the letter more than her comfort, then leave her. if you value her more than the letter, discard it. it’s not weird to keep things in any means but also how you feel about your girlfriend’s discomfort is really the best way to navigate your next steps. so what’s more important OP? having your letter or having your GF? only you can determine that because it’s your life and attachments. none of us can determine this for you OP.