There may be certain things you're doing that trigger your girlfriend's jealousy. While you can't completely cater your behavior to her insecurities, there may be certain behaviors you can tone down in her presence.  Ask your girlfriend something like, "Is there anything I do that makes you feel jealous?" See if there's a way you can help her feel more secure in moments where you inadvertently trigger her insecurity. For example, your girlfriend may sometimes feel jealous if you make plans with friends and do not invite her. You can try explaining to her that you sometimes need time alone with your friends, and this has nothing to do with how you feel about her. You can agree to remind her how much you value her when you make plans without her. Remember, jealousy can be very damaging to a relationship long-term. After listening to your girlfriend, you need to state your needs. She needs to take responsibly for her actions as well. Tell her how her jealousy affects you.  Say so gently. You do not want to provoke an argument. Say something like, "I know you don't like that I'm friends with Melissa, but I've known her since I was 12 and she was 10. I feel controlled when you don't want me to spend time with her because I value the relationship a lot." Be clear with your girlfriend about what you are and are not willing to do to reassure her. For example, you can agree to text her more often when you're out with friends; however, let her know you're not going to put up with her calling or checking in on you every five minutes. Jealousy is often the result of insecurity. Building up your girlfriend's self esteem can help ease some of her jealousy. Instead of getting angry when your girlfriend gets jealous, encourage her to work on bettering herself.  Allow your girlfriend to pursue her passions. Respond excitedly when she tries something new and pushes herself out of her comfort zone. Compliment her regularly. Let her know if you think she looks great in a new outfit, for example. Jealousy is a normal part of most relationships; however, jealousy can easily cross the line into unacceptable. You do not want to remain in a relationship with an unreasonably jealous partner, so learn to recognize the signs of over-the-top jealousy.  Does your girlfriend use jealousy to control you? Some people will use jealousy as an excuse for unreasonable demands. Your girlfriend may, for example, use her jealousy to keep you from seeing friends or loved ones. Unreasonable accusations are also a sign of over-the-top jealousy. Does your girlfriend accuse you of cheating without evidence? Is she constantly checking up on you or going through your stuff? If you believe your girlfriend is unreasonably jealous, seriously evaluate whether or not you want to stay in the relationship. Remember, you cannot control someone else's emotions. Know what your limits are. If your girlfriend's jealousy is pushing you over your limits, it's okay to walk away from the relationship. If your girlfriend is draining you emotionally, this is not fair to either one of you. If you feel like you're, say, answering insecure texts for days on end, it's okay to take a break from the relationship or end things altogether.

Summary:
Ask your girlfriend what things you do bother her. Let your girlfriend know how her jealousy affects you. Encourage your girlfriend to work on her self esteem and self confidence. Identify unreasonable jealousy. Determine your personal limits.