If friendship and love are based on something other than the best interests of both parties, then the consequences will be enmity. It can only be in their best interests if it is for the sake of Allaah.
Even though each one of them may be helping the other to achieve what he wants on the basis of mutual consent, this mutual consent counts for nothing, rather it will become mutual hatred, enmity and curses, and each of them will say to the other: Were it not for you I would not have done that on my own, so my doom is because of me and you.
And the Lord will not prevent them from hating and cursing one another, but if one of them wronged the other, he will be prevented from doing that, and each of them will say to the other: It was for your own purposes that you caused me to fall into this; like two who committed zina will say to one another: It was for your own purposes that you did this with me; if you had refrained I would not have been involved in it. But each of them damaged the other equally.