I read in a book on sexual abuse that when the abuse happens, that women tend to view it in terms of degradation. Feeling attention has to be sexualized ..even if with a married man. In turn, we feel shame at the sexualization and then further hurt ourselves. In the book it also talks about fears of intimacy that develop as a result of abuse and self-hatred. Because married men are unavailable, it might be easier to gravitate towards (also b/c it induces more self-hatred). Perhaps your own unavailability emotionally, allows you to give yourself to married men instead of single men for fears of being loved and fears of being known.
Just a thought..
Sometimes it is nice knowing that things you experience are common enough to be written about and may have a reason behind them. Hope you can talk to your therapist about it.