@George,
AnnieBananie~
OK, let's break this down.
Using
semper enim in corde meo to translate "for [you are] always in my
heart" looks fine to me.
Medullis means "marrow". It can also mean "heart",
but in the sense of the middle of something.
Now for
nos vero parte nunquam.
Nos means "we", but the personal
pronoun is seldom used as the subject in Latin because it is implied in
the verb.
Vero means "truly"; that's OK.
Parte could mean "partly", but
definitely not "we will part".
Nunquam means "never"; that's OK too.
~George