1) in case any complaint is filed against you contest it on merits
2) in your defence you can mention that lady had in presence of your relatives shouted at you and as result sent her the message only once in fit of anger
3) you had no intention to hurt her feelings and tender unconditional apology
4) police can trace phone calls . can summon records from service provider of calls made by you to your lover
5) lady may file complaint of criminal intimidation against you under section 503 of IPC