For LyX to work you need to install some kind of TeX distribution.

  - The print/teTeX port in the ports tree.
  - The TexLive ports in https://code.google.com/p/freebsd-texlive.

Either one should work fine.

***

As of version 2.0.0, LyX depends on the textproc/mythes ports for
thesaurus support. Even though the LyX port depends on textproc/mythes,
it is up to the user to install the thesaurus ports for her languages
of preference.