No definitely not. I think spouses can be best friends but to be honest I don't know of many couples who are also best friends. I tell my best friend absolutely everything as she does me. I don't do that with my husband - I like some secrets. Besides that I think a best friend of the same sex can be far more understanding and empathetic.
My late hubby and I definitely were, we could spend all day every day together with no bother at all, small separations like short hospital stays were really awful for us both.
Not sad at all planks. Mr LL was primarily my lover and the excitement in my life. I have to admit that is why I married him. We are definitely friends now though but not soul mates.
if my girlfriend were a chap I'm pretty sure they'd be my best mate, she has a lot in common personality wise with the closest of my mates but I'd definitely say she is my best friend. I've usually had a lot of good friends as opposed to one best so I'm not really replacing anyone.
So do I 4get. And she about her hubby too. I couldn't be without her although she is many miles away now (overseas) :o(. She is back home at the moment though. She has actually been a rock to me - the one who totally understands me.
Doesn't mean that you haven't got a happy marriage if you are not 'best friends' with your spouse though. Different relationships make different people happy.