Did Poseidon have any relationships with any gods?

Answer 1

yes.

Poseidon's brothers were Zeus and Hades. His sisters were Hera, Hestia, and Demeter.

well known children of Poseidon include the hero Theseus and the merman Triton.

Poseidon also had a "romantic" relationship with Medusa, but i believe this was before she was turned into a monster, and also the reason why she was turned into a monster. I should add that by romantic i mean she was raped by him, which for a male greek god was normal.

Like most of the male greek gods, Poseidon had many lovers and had many children with these lovers. His wife was Amphitrite, and she was a nymph. He also once hooked up with his sister Demeter.

Most of the greek gods were related, and inbred.