Both are valid it depends on context...
Someone loves Jessica - indicates that some person is unknown.
Somebody loves Jessica - indicates that the person is unknown but comes from a known group.
"Don't leave things in the car as someone could come past and break the window to steal them"
"Somebody in this classroom has dropped their pen on the floor"
The inherent vice of capitalism is the unequal sharing of blessings; the inherent virtue of socialism is the equal sharing of miseries. We contend that for a nation to tax itself into prosperity is like a man standing in a bucket and trying to lift himself up by the handle.