I believe in EA when you used Friends on someone during a dialogue they instantly became hostile and attacked you once the dialogue ended. You could avoid that by some cheese by teleporting away or something and waiting a couple of minutes. There was a whole topic about this here before.
My advice for the Friends spell is simple - if they didn't change anything from EA don't use it. It's not worth the hassle. Make a Character with high CHA and proficiency in Persuation and use Guidance and Enhance Ability spells.
