How to Do It My fantasy has become my nightmare. Photo illustration by Slate. Photo by lekcej/iStock/Getty Images Plus. How to Do It is Slate’s sex advice column.  Have a question?  Send it to Stoya and Rich here.  It’s anonymous! Dear How to Do It, My boyfriend and I have been together for about two years, and have both been interested in trying out a threesome. I found a trans girl who I liked and he seemed to like her as well and we went forward with it, but things didn’t turn out how I hoped and he only paid attention to her and not to me. I also seem to have developed an infatuation with her that I do not believe is reciprocated (she said she was bisexual but I suspect she might not be into cis women, or possibly just not into me). My boyfriend and I talked about things afterwards and he apologized but I still can’t help but have these constant memory flashbacks to him pretty much ignoring me the whole time.…