Did you actually have a boyfriend in the waking world when you had this dream? Typically, when there is a loved one in your dream, the dream reflects both yourself (the traits of your loved one that you most hate and most connect to), as well as how you feel about the person.

The basic actions are fairly straight forward - insecurity related to the flirting, a possible trust issue (provided there actually was a real life boyfriend), possibly a latent urge to flirt around yourself (like Pir said, everyone is you in your dreams)... The screaming is a reflection of a feeling that you can't communicate with the boyfriend (or possibly in general) well, often leading to shoutnig in an effort to have the person hear the message clearly. The girl teasing you is twofold. First, it could simply be the reflection of what you fear the girls boyfriend flrits with are making him think about you. Second, and mroe likely, are the latent feelings of low self esteem brought out from the flirting. If you are teh one that is flirting, this would equally apply, as the flirting can and is typically a subconscious attempt to validate and raise a feeling of value in one's self. The rage follows this twofold rule in that you are lashing out at both sources of insecurity.

The second scene is almost a follow through in logic (I say almost, because this is not how dreams operate, so it can't absolutely be attributed to this). This is where the fear of consequences is shown in the boyfriend leaving you, the initial victim, for this other person. Peculiar in this, however, is that if you consider that the girl is a personification of your own insecurities we find a distinct disengage that is equally as frightening as losing a lover. With your perspective looking on at the barely alive personification of your feared flaws, the you that boyfriend loves has become something completely else. On life support, your new self is something of a husk - hollow and empty of the life that you began with.

Jung said thaqt the goal of all psychology is the eventual assimilation of all parts of the self psyche. Here we have the male part of yourself personified in your boyfriend, the embodiment of your insecurities (the self image of you in your dream), and the shadow self (all the things about you you hate) personified in this other girl. Incidentally, the retaining of all three parts relies on the assimilation of the shadow self. Something you can do is consider the source of the other-girl character. Ask yourself what she wants, why she insists on belittling you, and how you can better be at peace with this other girl. Also consider the insults, and how they can be shown to be invalid. Remind yourself of the people that value you highly and those that love you for who you are.