Jealousy is a disease, love is a healthy condition. The immature mind often mistakes one for the other, or assumes that the greater the love, the greater the jealousy--in fact, they're almost incompatible; one emotion hardly leaves room for the other. But at once they produce terrible turmoil...
Robert Heinlein

Love may exist without jealousy, although this is rare; but jealousy may exist without love, and this is common.

Jealousy, that dragon that slays love under the pretence of keeping it alive.
Havelock Ellis