Defining Sexual Addiction

It sounds like you are really trying to understand yourself.  Good for you for being curious about your behaviors and wanting to better understand yourself. 

First of all, throughout your question, you keep stating that you have "always been a sexual person," so I'm trying to understand why you might want to change this now.  It's important to understand why you want to change this about yourself to better understand your behavior.  Are you wanting to be monogamous for yourself?  Are you wanting to be monogamous for your partner?  Do you think this is what you "should" be doing?  Do you think this is part of "growing up"?  It's imperative that you make sure you're doing this for yourself otherwise no matter what you do, you will be living up to someone else's expectations. 

Secondly, I would encourage you to talk to your partner about what is ok and what isn't in your relationship.  You seem to be asking me if it's ok to engage in sex chats on FB and on other sites.  For some couples this is considered cheating, but if you and your partner do not consider this cheating then that's between you two.  Many couples find different ways to express themselves sexually so I encourage you to talk to your partner about the "rules" in your relationship and respect them.  Some couples even have open relationships...it all depends on what both what from the partnership. 

I encourage you to also talk to an individual therapist about the role of sex in your life.  You seem to be in an exploratory phase and individual therapy could definitely help you sort this out.  If you are in the Los Angeles area, I'd be happy to help you: www.drlanichin.com.  Good luck.