Make sure there is no other way. Breakup SMS – an extreme measure, to which it is better not to use. Besides young person can receive the message for the draw or to fix that your phone got into the wrong hands.
The message is not obliged to be brief to monosyllabic, but an abundance of words you do not replace your own presence. On the contrary, the young man decides that you convince yourself of the need gap, so I doubt it. So select the brief statement. Write it on paper and try to read the eyes of her boyfriend. Consider it the state: angry, depressed, confused.
It expresses very clearly and concisely. Don't ask for "time-out", never delay.
Possible wording: "weekend stuff", "it's over Between us. I'm sorry," "I don't love you anymore" and so on the Context of SMS-correspondence does not imply explanation or showdown. You are just stating the fact.