I’ve been having this weird reoccuring dream, and im trying to become lucid so i can further explore it. Its pretty strange. A demoness (or some otherworldly female being) tries to posses me. I keep seeing wierd shit as I go through my normal daily routine, and eventually she becomes powerful enough to summon a full apparition. She follows me, and eventually, somehow (differs with each dream) we end up falling in love and having sex. What could this possibly mean? It couldnt be about any real life problems, as i have a beautiful girlfriend and great friends, but there’s some reason it keeps happening? Anybody have an idea why?
There could be many reasons why.
I’m not great at interperting dreams, theres plenty of way better people at this than me in the community, but I do know some basic stuff.
It could be related to stress, whenever I get stressed out, I tend to have bad dreams or a re-ocurring dream about a terrorist making a bomb in my old house. 
But it also depends, was the dream frightening? Or just strange?
Also, those dreams could just be a way for your mind to express itself because it’s been lacking that latley. You could try expressing yourself more.
Or, dreams are dreams, and this one happens to be re-ocurring?
If you look for a source to this dream, your GF might be the answer: You might be afraid to cheat her, since you don’t wanna hurt her (IE love her) and are afraid another “evil” woman will seduce you to cheating, even though you will try to continue your life normaly.
It could also mean - though I generally don’t think it is the case - that you want more interesting life, and are tired from your girlfriend: You want a change with a new, “exotic” person instead of your girlfriend, but still you want to avoid leaving her and prefer to be “possesed” and falling in love then just breaking up with your current GF.
To conclude - I believe your dream is of the first option, though it is based only of what I know of you. If you could tell more about how long you have been together (Not so long, I persume - a few months), how you feel about her (deep love?) and how do you feel about other girls It could be better understood.
One more thing that has occured to me - you might want to have a girl in addition to your GF, which is causing you great confusion as you cannot do such a thing.
Anyway - just remember: We can only make suggestions. We don’t have even a fraction of the info you have about yourself, so eventually, only you can interpret your own dreams. Just don’t hide anything from yourself!
Pretty much… What does a demoness mean to you? The symbols work with what YOU think of them. So a fantasy writer would think differently of a demon than an extremist catholic would.
Have you changed your behaviour since you got your girlfriend? Sort of, going against what you would otherwise want to do. Saying weird things you wouldn’t otherwise say? In a way, taking on aspects of her personality in order to get along with her? So the dream would be a subconscious expression of resentment. Getting possessed, or controlled. I know you’re probably thinking , “no way! I don’t feel that way”. But that’s why they call it the subconcious. I noticed you mentioned your girlfriend first, why was she the first thing you though of, when condering problems? Just a thought, though I feel like I am making a case here. Don’t take me seriously, please!