From what I know of her Demeter is not married to anyone, but she has had nine children (both by mortals and gods.)
love and beaty
We will never know. The Greek goddess Demeter was immortal and so never died.
She did not marry anyone, but had Persephone and several other children by Zeus.
Demeter was never married but she was in love with Zeus pre-Hera.
Poseidon gave Demeter a magnificent white horse named Arion as a gift to win her love.
agriculture
No, but hades did kidnap Demeter's daughter.
no they were not because Demeter love her work and was not able to do any think but care for her daughter and the land,
Loss and love: the loss of Persephone from the Earth goddess Demeter, the love of Hades for Persephone, the love of Demeter for Persephone.
ZeusPoseidonIasionKarmanorTriptolemusOceanusDemeter has relations with these six men/gods
Hades fell in love with Demeter's daughter, Persephone. So while Demeter wasn't looking, he kidnapped Persephone and took her down to the Underworld. There, he made her his queen.