Application as a parent of a British child

[Papito213]

I am the Father of a British child but mother of the child has been separated from the ex-husband for over 5 years but not yet divorced.
Can i apply or still apply via the parent route - FLR FP, even as my partner has not divorced from her ex-husband? What documents will I need for this application? Will her non divorce prevent the success of the application?
Will the mother’s marriage to the separated husband be considered during the application.
I currently do not live together with my child and his mother but visit them very often and has been very supportive to them.
Please advice and help needed urgently.