You Rang?
The "friends first" works for some.
Anytime you involve anything more than physical pleasures into your relationship you take the chance of attachment and drama. That is just how humans are.
Laura and I have all the "relationship" we desire within our own relationship. We do not desire to deal with any further attachment from anyone outside of our relationship.
We see couples coming here crying about the "break up" of their couple "friends" that they have developed over time. We really don't need that. There are enough emotions between us in every day life, we don't go out looking for more.
You have to do what works for you but you have to keep in mind, if you involve more then just fun sex you will end up at some point with emotions, drama and heartbreak involved.