Responses
Only answer I can think of is it being so good that they can't control themselves ლ(´ڡ`ლ)
In all seriousness probably prepping and how it isn't always easy to get used to anal ٩(๑❛ᴗ❛๑)۶
What does he mean by sex would be really risky ?
http://www.mangago.zone/read-manga/blue_lust/uu/d_v-3-chapter-14/pg-12/