He has a long history of dating / marrying very young women. His first wife (the one you referred to as getting left) was 15 when they officially started dating. He first met he at the age of 12. She was pregnant by 16.

There's also the weirdness of how his movies portray age gap relationships. The professional in particular is often criticized for how it both sexualized a young girl & portrayed her as the instigator. Natalie Portman has talked about how this movie brought her fame and long lasting trauma. Plus the original cut was much more problematic & the studio cut quite a bit before it was released -- so bussons original vision was even more pedophilic. Plus it is supposedly inspired by his real life romance with a 12 year old.

Here's a link to a essay that goes a bit more in depth: https://faroutmagazine.co.uk/luc-besson-leon-the-professional-truth

Edited to add: there are also the many rape allegations from various women who have worked with him over the years.