A frienship is a type of relationship.

^^very true.

But a normal friendship is where you share a bond like that of a brother or sister, someone you wouldn’t see in a romantic light. A relationship (like boyfriend/girlfriend) is where you do see them in that way, it’s basically just a difference in they way you are close to them, not how close you are.

It’s a spiritual thing. A friendship is being part of their life. In a romantic relationship, you feel like you’re part of them.

It’s hard to explain these things without resorting to poetry!

Obviously, friends can become lovers. It is not a natural progression. There is no specific point when you make the leap. I suspect you have a friend that you are considering as a lover. It’s a tricky situation. Most relationships, both friends and lovers, are terminal. So what the hell – go for it.

Genitalia is the difference for me.

You’ve touched upon the answer to your own question in the explanation: sex (but not always exclusivity, multiple partner relationships are known to exist; and many people opt not to have children).

Your relationships with other people can vary from acquaintance, to friendship to romantic involvement. There are many sub-sets of relationships.

Friendship is a relationship and is a component (I sould hope) of romantic relationships. I believe the difference between friendship and a relationship is the depth of the bond and the emotions evoked between you. I would say sex, kids, and exclusivity are not capable of defining the difference.