How can one deal with the desire to marry a girl with a non-committal past, and is it acceptable to be associated with her while she is still in another relationship?

Befriending girls is evil and a path to temptation and corruption. The hadiths have warned against the temptation of women. Showing feelings of love and communicating with girls can be a cause of temptation and straying from guidance. For safety, all relationships with girls must be severed. It is best to wish the girl repentance and supplicate for her. There is no harm in proposing to her if she repents, while being keen to utilize time for what benefits in religious and worldly matters.