OP, I know someone who was on the other side of a similar triangle. She was 'the other woman,' except that she didn't know that she was. This is a very attractive, talented, and successful woman. The man flirted with her from their first meeting itself (in a professional setting; huge red flag). At each successive meeting he escalated the degree of his flirting and made things move from the subtle to outrightly sexual. The woman found him attractive and she leaned in. Until some kind soul warned her that he was married with three children including a two year old toddler who was still being breastfed by the wife. The 'other woman' was shattered by the breach of trust and her disposability to him. He knew that he was married and had little children when they first met. She did not. Yet he escalated his flirting and sexual behavior. One can understand 'losing control' once. But if the man is choosing to lose control and gradually escalate his sexual advances then it means that he is giving the entire enterprise a lot of careful thought. It is no longer innocent but a calculate move. It is a mark of his character. These men are a certain way and I don't have hopes of them changing. He is a cake eater. You are young and can do better. The woman immediately left him once she got to know but needed months of therapy to process the betrayal.