Why do I get so jealous?

then you are a little confused first you complaint about him being with his friend and then when he offers not to be with his friend you tell him it's ok be with his friend. you need to be clear on what you want. another thing jealousy is insecurity about something that some one else has and you can't have the same thing. may be you need a friend for when his friend comes over that you and her can go out together. or maybe get a friend to go out with him and make it a foursome. and jealousy is not healthy if you take it too far or dwell on whatever you are jealous about.