My girlfriend and I have been together for over 5 years and will be together for many more. After much hesitation, I confessed my fantasy of watching her with another man one night during foreplay.
If you kept your fantasy centered on watching her with another man instead of being an active participant in a "menage a trois" centered on giving her pleasure, this could cause her to be hesitant as many women don't wish to be made to feel as though they are performing. They want their man to be part of making them happy.
She had me play with her clit while telling her about what I had fantasized, its hard to describe my feelings during the act as I was excited but also more than a little unsure. She got very wet while in the act but in conversations that followed, she was more into the idea of bringing in another girl (doesn't suck).
This is sounds extremely promising as you are both clearly able to be open with each other and enjoy each other's fantasies.
The fact that she introduced having a FMF threesome rather than a MFM is also a good sign as most women don't like the idea of having a MFM when their partner brings it up because they are afraid he is only doing so to eventually get her to "pay him back" with letting him have another woman. Your lady seems very self assured and adventurous. She may also have curiosity regarding bisexuality with another woman that a FMF could help her entertain.
When you say "doesn't suck", I assume you mean your girlfriend doesn't perform oral on you.
If that is correct, then it seems she is also caring about your desires as well. There are reasons many women can't perform oral sex, some physical (TMJ), some psychological (trauma of baby abuse). Whatever her reason, the fact that she is willing to bring another woman into your sex lives to do this for you is outstanding.
All good signs.
Im not sure if/when this might happen for us, but being able to confess this desire to her and her being open and receptive about it really made me feel a lot closer to her. I don't know if this will happen or not, but the fact that it created a new level of closeness between us was worth bringing it up. Love this site so far and the people I have spoken with
This is really the main focus, having a strong loving relationship with open, honest communication. If you have that, the two of you can do pretty much anything.
Best of luck to you both, although I doubt you need any more than you already have. Sounds like you will have a wonderful life together.