I re-read some of Christopher Pike's more sci-fi leaning books from my teens, namely The Tachyon Web, Sati, The Starlight Crystal, The Star Group and The Visitor. The last one is the most on the horror side which just makes it silly, and it's not well explained. I think I'll stop there. His horror books were what we read when we wanted to feel more grown up than Goosebumps readers. I kept collecting them obsessively while my friends moved onto even longer, more gory books.
I could've sworn one of the books had a bit where someone gets it on with an alien and has an out-of-this-world orgasm, but I have no idea what book that was now. I thought maybe it was Sati as that one seemed to be marketed more towards adults, but nope, that just seems to be in the sense that it's kind of a spiritual/religious message and nothing very exciting happens in it. Must've been something else I read around the same time.