Based on the comment from 1_Vee_0

You are Frank's older/younger brother/sister. Despite frank being gay, you and your parents always gave him the unconditional love and mega support.

Whenever you see frank having many encounters with eddie dear, the mailman, you would always fanboy/fangirl at frank finding a special someone. This got frank to be embarrassed. This had happened for the past many years. That is until finally you got a cheeky idea when you see eddie and frank hanging out as usual.

You: time for me to set up a wedding!
Frank: no! Don't you dare!
You: too late, big/Lil bro. I already bought flowers and invited the guests! And you're gonna wear a dress! *devilish smirk*

Frank ran off in embarrassment.

Eddie: frank! *runs after frank* wait for me!

You and the entire neighborhood laughed until you all cried.

The day of the wedding. Your father led frank to eddie, much to Frank's embarrassment. Frank wanted to get back at you for planning a wedding. The wedding ceremony went on well and eddie and frank sealed the vows with a kiss. Then the party began. Frank stood next to the cake and got a cheeky idea.

Frank: everyone, I would like to give a big thank you to my older/younger brother/sister, y/n l/n. Without his/her support, I would have never had married anyone special in my life. As a thank you, here's the gift.

You open the gift from frank when it's revealed to be your crush who came out of the box to surprise you!

Crush: hello, my darling! When's the next wedding?
You; *runs away in embarrassment* NYAAAAAAHHHHHH! I HATE U SO MUCH FRANK FRANKLY!

As your crush ran after you, everyone, including your parents, laughed so hard until they cried.

Frank: that's karma for my sibling! Eh, eddie?
Eddie: You bet, dear husband.

Eddie and frank kissed passionately.