If they are still texting each other more than 6 months after you came along then they were/are more than **** buddies.

Friends, friends w/benefits or whatever they have now is making you feel uneasy, correct?

You didn't put her in this "awkward space", she did. Expecting you (or anyone) to be o.k. with her continual contact of a past lover is unreasonable and disrespectful of your feelings.

You will never feel secure if your partner is forever reminding you that she has options. Unless you want to be forever policing her behaviour, i would move on.