The script most heterosexual couples follow is: erection, penetration, ejaculation. Sex ends when he comes. Her pleasure is systematically decentred. If you don’t flip that script and centre her pleasure (think lots and lots of kissing and boobie play and generous oral and fingering, and toys and eye contact and penetration for as long as she needs, and just the way she likes it, and multiple orgasms for her before you even think of coming) then all she’s getting is porridge