Matthew 18:10 and Psalm 103:20 are two places to which the Catechism of the Catholic Church points when considering the presence of angels. Matthew 18:10 ("Their angels always look upon the face of my heavenly Father") is said of children, but the Catholic Church extends that to children who are growing and are grown up as well. In the Book of Daniel, angels support Daniel in his trials. The Jewish people have long believed in angels and that belief has actually been expanded in Christian circles. Look up angel using a Scripture index--and you will find many angels assisting humans--and that is the essence of a guardian angel, even if that particular word isn't used.

I believe that you can name your guardian angel yourself, if your desire for a close friend is accomplished by acknowledging the presence of your guardian angel. I feel certain that your angel will accept your loving choice as a "nickname" and you will experience a new closeness. Remember that angels are just one of countless expression of God's love for you. God is your ultimate guardian and God's arms are big enough to hold EVERYONE! Humans like to feel "special" though and angels have been sent as extensions and expressions of God's all-encompassing love. Angels point you toward God, whose servants they ultimately are.

More about angels is available in this section by checking other response to similar questions.