Are you sure that you actually installed the X Windows System? During the installation of FreeBSD, you've a bunch of options like:
Developer = This does not include X Window System
X - Developer = Same as above + X Window System
Kernel Developer = Without X Window System
X - Kernel Developer = Same as above + Window System...
Just in case that you've missed that one
. This is freeBSD but that might be similar to Darwin, since Darwin is BSD based(???).