Can I be and call myself polyamorous even when I have never been in this type of relationship before?
Of course. Few people ask whether they can assume they would be happy in a monogamous marriage before trying one out. Little kids daydreaming about a wedding/marriage are never told "you haven't tried it, you don't know." Little boys assuming they like girls are not scolded because they have never been in a straight relationship before. You know best who you are. As in all things, stay open to experimentation; don't get locked into an identity that stops you from growing or living intentionally. But the answer to your question is yes. Check my FAQ on this here.