the thing you have to ask, are you willing to lose that friendship if the relationship fails. Id rather have a good friend I can trust, than an Ex.
It's good to be best friends with your partner.
Well if you are already thinking about that then you're doomed for failure.
most relationships fail. no amount of positive thinking will change that.
That's not entirely true. If you are compatible with someone and you feel good about a relationship positive thinking can be the only way you stay together, especially if there are a lot of people that doubt your relationship and push negativity upon something that doesn't concern them.