A female gives a titjob to her manfriend. Just as he is about to ejaculate he turns around, shits on her neck and ejaculates into her bellybutton

A jack off buddy (from 'cum' /'come', meaning 'semen', and 'companion'); a friend that you get together with for sessions of solo or mutual masturbation
Variant of: cumpanion (from 'companion' & 'cum'); jack off buddy & wank bud & JO buddy
Similar to: fuck buddy