Thesis 1: There is no special form of love that falls under the label "friendly love" or "the love characteristic of friendship". Every love is a friendly love.
To love someone involves appreciating the beloved, pursuing her good, and seeking some sort of union of common pursuit with her. If we have only one out of three then we do not have love, but something else, respectively like disinterested appreciation, benevolence or lust. Nor are two out of three enough. But if one has all three, one has friendly love. For friendship is multiform, and any common pursuit providing a genuine union can be made the object of a friendship.
One might try to distinguish "friendly love", however, by its mutuality. While one can have unrequited romantic love, one cannot have unrequited friendship. Friendship is essentially mutual. But this argument is invalid, since friendship is not the same as friendly love. Friendly love is the love characteristic of friendship. But it can exist without a friendship. If I am your false friend, but am a very good actor, we can have what from your point of view looks just like friendship. And your love does not fall short of friendly love—it is my love that does so. So, you have a friendly love, even though there is no friendship. Or consider cases where the friendship has been lost, because one party has slid into vice, but the other retains a friendly love, striving to rescue the backslider.
The distinction between friendly love and friendship is essential to Plato's Lysis. The Lysis begins by attempting to define a friend (philos--the noun) in terms of friendly loving (philein--the verbal form; I am suspecting that philia is ambiguous in the Greek between friendly love and friendship). We begin by rejecting the definition of a friend as someone whom one loves with friendly love or someone who loves one with friendly love, on the grounds that if the friendly love is reciprocated with hatred, we do not have a case of a friend. This argument requires that it be possible to have a friendly love that is reciprocated with hatred, and hence that it is possible to have a friendly love without friendship.
Thesis 2: Friendship is the right kind of mutuality in friendly love, i.e., in love.
I do not know how exactly to characterize this mutuality, though. Minimally, it requires that each should know of the other's friendly love, but more than that is needed.
A consequence of this is that appropriately mutual romantic love is a kind of friendship.