Chances are that he is in fact in your contants but as a suggested
contact. If he wasn't in your contacts at all his email address would
not be suggested :)
Google contacts are seperated into two "groups", My Contacts and All
Contacts. My Cintants are the contacts that you have either physically
added or told the contact manager to add. All Contants contains just
that, ALL your contacts whether you added them or GMail is just
suggesting them because you've sent an email to them before.
I would suggest looking in All Contacts for your associate and either
remove him or move him to My Contacts (after changing his email
address of course)
--
-Nick