oh man i literally JUST read an article on askmen.com about all of the texts not to send this definitely falls into that category..
it also reminds me of that sex & the city episode (yes, i watch that show, don't hate) where burger leaves carrie a break up note via POST IT!! "i'm sorry, i can't, don't hate me."
honestly, i am so sorry you had to get that text message..there's no excuse. some things are easier not said in person, in that case, don't say them at all; rather, wait until you are brave enough to say them in person.