Our relationship started as an open one, which was fine for all parties involved. After a few months of this and us becoming very close, I'm beginning to feel somewhat hurt and upset when I know she's with another guy. Things have progressed to a point where we consider each other best friends, and we tell each other everything - even if we don't necessarily want to hear it, for the sake of retaining an honest relationship.

I have confided with her at this point that I get upset when she's with other people, and that my feelings for her are such that I'd like a relationship. Her response to this was that she's not ready. This is perfectly fine. She has a right to explore the world and be comfortable in her sexuality; however, my dilemma is that although it has become emotionally difficult to handle this openness, I don't want to lose her. What should I do?

You don't HAVE a relationship if she's with another guy. Do you like sloppy seconds? You only THINK you are having one... she clearly has other ideas about that.

How much time do you plan on wasting? 2 years, 5 years? 20 years?

Time to find someone who isn't taken.

You can't lose what you don't have and may never get what you want from her. She may never be ready so explore other options. If you cannot handle her program, get one of your own that doesn't include her or be stuck forever in your own crap.

Sorry guy, you have a decision to make. I would leave her alone until I could be a healthier more objective friend, or at least get my feelings in order, and keep my dignity and self respect.

She is not yours to lose.
Leave her alone or keep hanging on like a lovelorn puppy.

'my dilemma is that although it has become emotionally difficult to handle this openness, I don't want to lose her.'

We rarely get what we want. You have to choose between the short term pain of breaking it off vs long term suffering of staying the dreaded 'just friends.' I agree with all the others - you are just a lovesick puppy at this stage, and need to get out now.