I believe love only comes from understanding the other party.
You like him not just because of her outward appearance, but his
inner character as well. You would enjoy his company, want to go
out with him, appreciate his good points and willing to accept his
bad points. Even deeping, its mutual understanding, consider his
interests more than your interests, having mutual trust, able to
forgive him whenever he has done wrong and willing to share your
life with him to go through any obstacle in life.
Love takes time to cultivate, it does not come immediately, coz you
need time to understand him as well.
Love can come from a crush as well, provided the other party is
interested in you as well. A crush might not turn into love, coz
you may like him initially, but after you discover his bad points,
you find that you cannot accept him.
Regarding that long time buddy, if you find that you understand him
enough, u enjoy his company and you allow yourself to discover him
more, it can develop into love as well.
There are no definite answers to love. There are only guidelines to
follow, the rest is up to u to discover.