Your use of "just really" in this line of your poem, "That should be just really how a friend should be," is perfectly all right. As many adverbs as needed can be used in quick succession by a writer to express what's in her or his mind, as in "I love you deeply, maddeningly, consumingly, desperately, distractingly +...ad infinitum." There are no hard-and-fast rules on the number of adverbs that can be deployed for self-expression. The only limiting factors are risk of wordiness and the need for prudence and self-control. Indeed, a sixth sense is a must--it could take some time to acquire and develop though--for how much adverbial modification the listener or reader can take in a given situation.
