Seiso na Kanojo wo Nakadashi Chuudoku ni Saseru made

A prim-and-proper girlfriend who's never had any sexual experience with men, until now.

It's been three months since he started dating her. Up until then, they've always stopped at just kissing; intending take their relationship to the next level, her boyfriend gathers his courage and asks her for sex. She also feels that their relationship shouldn't remain stuck at that point, and so she gives him her consent. However, he doesn't wear a condom for her first time having sex...

Even as she tries to resist getting creampied, her body quickly turns on her to accept it and this sequence becomes a repeating occurrence.

(Source: Melonbooks, translated)