What you describe is a much more common condition than most would admit. Many men have issues with jealousy and possessiveness. It is often linked to our own self views, past trust issues (with significant others) like family, and a lack of emotional security. Some men develop this because of past abuse and experience it as a traumatic reaction to that abuse.
No matter the reason, you have taken an excellent first step, that is reaching out and admitting the problem. It may not seem like a lot, but most men refuse to do this and as a result, stay the same, unchanged.
You sound serious about getting rid of this issue: If so, I would like you to start with a good resource: Overcoming Jealousy and Possessiveness [Paperback]Paul A. Hauck
This is a very inexpensive book on amazon.com and will help you begin to set this right.
Jealousy and insecurity operate in "darkness" in males. Simply, they are issues that we do not often admit to others and as a result they remain untreated. The emotions thrive with this environment of non-disclosure. To drag this issue into the light is the beginning of its death. To do that effectively you will need accountability with another person. The best one is a cognitive behavioral therapist, a person who is specially trained to help you reorder your thoughts and get past whatever prior influences helped shape you in to a jealous person.
Take heart! The steps outlined here will get you on the right path. You will be much better in short order. Therapy is very helpful and the book will start you on the path to recovery. Steven