i know it's frustrating! my stbx always brings the gf/ow to pick up or drop off my kids. he brings her to school functions and sports activities. he has her write the infrequent support checks. yes, it bothers the shit out of me, but i don't let on to him. i just vent to friends or here. don't let her know it bothers you. take the high road. remember, you are better than that!