Storytime.
The campaign is Waterdeep: Dragon Heist. After being shunned by her family, my insecure half-orc cleric has fallen into split-ownership of some property, that she and the party finally settled on a plan for and made into a high-class club we called 'the Rising Tide'. Her crush (a buttoned-down and illegitimate, but very attractive, tiefling scion of some local nobles) showed up for the grand opening, and during their conversation, he assured her that a letter would be pretty welcome.
So the next day, when she spied a story about him in the local yellow rag, she took it as an opportunity. In short, she wrote something like "Hey, we all know the quality of story this idiot prints: I don't believe it, and I doubt anybody else does, but if you want to keep people from speculating on your romantic status, I'd be happy to hang around with you and discourage any admirers with ill intentions. HINT HINT."
Fast forward to the END of that day, after she and the rest of the party have spent several hours crawling through literal rivers of sewage, fighting gross monsters, and not getting very far on the actual plot. When we got back home, there was a letter waiting for my cleric--a reply already! Faster than she had ever moved before she ran up to her room, squealing "He wrote me baaaaaaack!" And spent the rest of the night cleaning up, reading, and re-reading her letter.
Yes, it turned out well.
Having an NPC write a love letter sounds to me just like having the guardsman tell everyone how it is his last day on duty and he can't wait to retire to sit on the shore of his favourite lake and fish in peace.
Would be a shame, if something... happened to them.
In my Call of Cthulhu campaign, a character received a cathartic, romantic love letter from his long-distance sweetheart NPC. And then the PC was killed in one shot by a sniper in the next episode before being able to write back.
It's a lot. The dice are cruel sometimes in high-lethality systems but it's made a great tragedy for the other party members- they have to share the bad news when they get back to town, and that's some juicy horror/drama roleplaying.
After an evening of wining and dining you're invited up to their room at the inn to stay the night. After fading to black the DM asks for a con save. Failing the save you awaken in a bathtub filled with ice sometime after noon missing a kidney.
