"He kisses his girlfriend in the forest."
Translation:Li kisas sian koramikinon en la arbaro.
Shouldn't it be "Li kisas lian koramikon..."? Unless we're to assume she's not his own girlfriend but some other girl's girlfriend?
lian would imply some other boy's girlfriend, ŝian some girl's girlfriend, and sian his own girlfriend.
Were you confusing sian with ŝian, perhaps?