[M]y ex came to visit [F]riends but ended up cheating on her future husband

My ex girlfriend from high school (one I lost my virginity too) came home one weekend to visit her friends from school. We had been separated for about 4 years at the time and hadn’t talked because her family moved away shortly after we broke up. I saw her at a local restaurant when I went to dinner that night but didn’t speak . Around 9 that night I received a text from her asking why I didn’t come and say hey and I explained that I knew she had a boyfriend and didn’t want to make things awkward with her friends. She said nonsense and we proceeded to catch up over text. After awhile I told her I was running out of data (2008 ?) and couldn’t text much more but she was welcome to come over and park across the street and I would sneak out (We both come from strict religious family’s that don’t allow significant others over late) to talk to her. She agreed to come over but said that it was just to catch up that she was in a serious relationship and I promised her I would be good?.