In the first scene of Act 4, the audience finds Belvile imprisoned in Antonio's house after he's been wrongly accused of injuring Antonio in a sword fight. Arrested for Willmore's crimes, Belvile fears that he will now be unable to find Florinda before she's married off to Antonio. The scene opens with a soliloquy in which Belvile personifies fortune as he bemoans his bad luck:
When shall I be weary of railing on Fortune, who is resolved never to turn with smiles upon me?
This first line of the soliloquy is a rhetorical question in which Belvile expresses that he's tired of complaining about his misfortune—something he feels that he's been doing a lot recently. Instead of referring back to fortune with a "which" in the second clause, he refers to it with a "who." He then claims that fortune has decided never to turn with smiles upon him. "Smile upon" is a phrasal verb that means to regard favorably. Taken literally, the smiling upon contributes to the personification of fortune. Taken figuratively, the smiling upon underlines Belvile's impression of his own bad luck.
This personification returns at the very end of the same scene, when Belvile apostrophizes fortune in another soliloquy:
Fantastic Fortune, thou deceitful light,
That cheats the wearied traveller by night,
Though on a precipice each step you tread,
I am resolved to follow where you lead.
Belvile addresses fortune and compares it to a deceitful light that misleads travelers at night. In this metaphor, the traveler in question is himself—he feels that he consistently finds himself in challenging situations that aren't his own fault. However, it is also possible that he's suggesting that Antonio is being misled by fortune's deceitful light. Earlier in the scene, Antonio has instructed Belvile to fight on his behalf in a duel over a maid. Belvile is sure he is speaking of Florinda. If fortune is playing tricks on Belvile, it is without a doubt also playing tricks on Antonio, as he doesn't realize he is asking his rival for Florinda to represent him in a duel over her.
Belvile concludes his apostrophic personification of fortune in the last two lines, stating that though it may take him down dangerous paths, he has no choice but to follow it and see where it will lead him. The character's personification of fortune in these two soliloquies underlines that he is both frustrated with and accepting of his circumstances. Ultimately, Belvile is a brave and experienced Cavalier who recognizes that one cannot have control over all that happens in one's life.
