I could say a lot about this, but it would only pertain to Bill and I and what works for us easily doesn't work for another.
Great friend and lover? Check.
Everything else is pretty subjective...
We both love co-existing, which means each doing our own thing together, if that makes sense.
We're monogamous (it requires both to want that in order for it to work), but that means little when considering all the successful relationships that are not.
We have no secrets from each other. We gave up privacy for each other, then gave it back to each other as a gift of trust.
I could go on but some readers may go into diabetic shock, lol.