Well....
Me And My Boyfriend Spilt Up 2 Weeks Ago, And Its His Birthday Soon, We Are Still Talking And He Wants Me To Come Down To His, Anyway We Used To Write Little Messages In Our Birthday Cards And Valentine Cards, Know I Have No Idea What To Put Help Please....:(

"I am sorry that things ended up the way they did"

Then purchase a stamp and put in the mailbox

You are no longer together, so just say "happy birthday", and mail it, and be done with it.