Final answer:
The kind of love that gradually evolves into a stable, best-friends type of companionship is known as storge. This love style is similar to Aristotle's concept of friendships of character, and it strongly correlates with human flourishing or eudaimonia.
Step-by-step explanation:
The style of loving that represents a comfortable, best-friends kind of love which grows gradually to create a stable and even-keeled companionship is b. storge. This type of love is akin to what Aristotle mentioned in his Nicomachean Ethics as friendships based on an appreciation of someone's character. These friendships, and by extension storge love, are robust as they are rooted in the mutual recognition and desire for the other's good, contributing to human flourishing or eudaimonia. In contrast to other styles of love like eros (romantic love), ludus (playful love), mania (obsessive love), and pragma (practical love), storge emphasizes a deep connection that is slow to develop, aiming for the well-being of the individuals involved, and aligning closely with the ancient Greek view of eudaimonia.