The definition of "first boyfriend" or "first love" can vary depending on individual perspectives and experiences. In your situation, you were in a romantic relationship with this person for three months, even though he didn't want to officially label it as dating. During this time, you had emotional involvement and a connection that resembled a normal couple's dynamic.
Whether you consider him your "first boyfriend" or "first love" is ultimately up to you and how you interpret the significance of the relationship. Some people might see the label of "first boyfriend" as being reserved for official, exclusive relationships, while others may consider the intensity of emotions and experiences they had with someone as more important than the specific labels.
What's most important is what you learned from this experience and how it shaped you as an individual. Relationships, regardless of their duration or label, can be significant learning experiences that contribute to personal growth and understanding of oneself and others. Take the positive aspects from this connection and use them to help you make future decisions about your relationships and personal development.