My younger brother cleary wants to fuck me

Since I discovered I was a trans girl and started HRT (1y and a half ago), my brother (19 years old, 1y and 3 months younger than me) has been asking me to "help me feel like a woman," which is clearly a metaphor for sex. I'm tempted to accept, but I'm afraid our family will find out, or that is going too far, like, we are siblings in a christian family, he always supported me on my transition, but I've started to feel a strong attraction and have even touched myself thinkin about him. I'm have been thinking to talking to him about it this week, maybe... giving it to him as a "Christmas present"