Simp
simp; someone who fawns excessively over a love interest (mocking internet slang)
Origin
Anglicism from internet culture, derived from 'simpleton' (fool, dimwit). Already in 1980s/90s hip-hop culture 'simp' denoted a man too submissive toward a woman. Via platforms like Twitch and YouTube the word became popular: a 'Simp' showers the of their affection with attention and favours without it being reciprocated. Hence the 'simpen'. The term is partly criticised as sexist.
Examples
Er kommentiert jedes ihrer Fotos, totaler Simp.
He comments on every one of her photos, total simp.