Licking My Step-Brother's Asshole

I'm in a state of panic right now. I'm in a dilemma and unsure of what to do. Recently, my partner, whom I deeply cherish and fear losing, has expressed a desire for me to engage in an intimate act involving his rear end. This is totally new territory for me, and I'm feeling extremely anxious.
I can't turn to my girlfriends for advice because I'm afraid they'll judge me or spread rumors at school. Teenage girls gossip a lot, and I don't want to deal with that drama. The only person I feel comfortable discussing this with is my step-sibling.
We've always had a close bond, and he was the first person I confided in when I lost my virginity. Seeing my apprehension, my step-sibling sensed that something was bothering me, especially after I made sure our parents were occupied downstairs. After beating around the bush for a while, I finally blurted out that my boyfriend requested a specific intimate act involving his backside.
Even my step-sibling, who knows me inside out, was momentarily speechless. Things took an unexpected turn when I mustered the courage to ask him if his partner had ever engaged in similar activities with him. He was initially hesitant to share, but upon realizing I was serious, he confessed that she had.
In a moment of impulsiveness, I made a request that I never thought I would ever make. I asked my step-sibling if he would allow me to explore this act with him, to lick his backside. Witnessing my step-sibling parting his legs and baring his backside for me, I leaned in and ran my tongue along his exposed butthole.
The sensation of licking his backside aroused me more than ever before, and I noticed his arousal growing evident as well. Without hesitation, I began stroking his erect member while pleasuring his rear end. He then reciprocated by pleasuring me in a similar manner.
By this point, we were both consumed by desire, oblivious to the fact that our parents were downstairs. I eagerly welcomed his penetration as he entered me, and the pleasure surpassed anything I had experienced with my boyfriend. His throbbing manhood penetrated me deeply, eliciting intense sensations with every movement.
Ultimately, I brought him to climax by tonguing his backside and stroking his pulsating member until he released in my hand and on himself. Even if I were to fulfill my boyfriend's desires, I doubt it would compare to the intense encounter I shared with my step-sibling.