What does sooner or later he must needs be mine mean?

The phrase "sooner or later he must needs be mine" suggests that the speaker believes that, eventually, the person in question will belong to them or be in a relationship with them. The use of "must needs" implies a sense of inevitability or necessity, indicating strong feelings of desire or destiny. Overall, it conveys a deep conviction that, despite any current circumstances, the bond will ultimately be fulfilled.