I texted my ex gf in a offensive word, she threatened me back by saying she will report to cops?

Contact a creminal defense lawyer. You say your words were "nasty" and her words were "ofending". Funny how much harm can come from words. Cool it on the texting

In Texas, a person commits the offense of harassment if "with intent to harass, annoy, alarm, abuse, torment, or embarrass another, he:
(1) initiates communication by telephone, in writing, or by electronic communication and in the course of the communication makes a comment, request, suggestion, or proposal that is obscene;
(2) threatens, by telephone, in writing, or by electronic communication, in a manner reasonably likely to alarm the person receiving the threat, to inflict bodily injury on the person or to commit a felony against the person, a member of his family or household, or his property; [or]
...
(7) sends repeated electronic communications in a manner reasonably likely to harass, annoy, alarm, abuse, torment, embarrass, or offend another." Harassment is a Class B misdemeanor, carrying up to 6 months in jail or probation for up to 2 years and a fine of up to $2,000 (unless you've been convicted of harassment previously, in which case it's a Class A misdemeanor).

You need to hold on to the text messages you have from her as well as your phone records (the company can only record that a text message was sent or received; they do not keep the content of the message). The police can wait up to 2 years after the date the crime was committed to file charges against you for this offense. If they contact you and want to speak with you, I would discourage you from doing so (anything you tell them WILL be used against you at trial) and suggest that you speak with a local criminal defense attorney as soon as possible.

Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.