What's the first step toward being authentic in a relationship with my bf?

Relationship. Be truthful, tactful and listen with an open mind without trying to fix or make judgements. Empathy, the ability to understand and respond to the unique experiences of another, is the most important capacity to develop and improve to maintain a lasting intimate relationship. Authenticity is central to being empathic. Best.
Trust. Trust is perhaps the most important aspect to have before one can risk being authentic in any relationship. Another factor is a strong, positive self-image and self-confidence.