Whoa! You've got a lot going on here.
I have so many questions. You say that you were a virgin until two months ago when you chose to give that priceless gift to this woman. I wonder why. Do you see in her your life partner? Are you absolutely certain that she is the person who will share your love and help you to become the best possible person? Is this your "soulmate"?
If not, why are you willing to give so much of yourself to her?
If the answer is yes, then I wonder why she is placing so much focus on sex.
I have several concerns about the relationship that you have described.
She tells me that she loves for the guy to know what he is doing, and that I just can't do that. She says, "I'm getting better, but not where I need to be." She says, "I just don't move right." She has her orgasms, but she says that our sex could be a lot better. This has caused a gap in our relationship, and she wants to date other people.
Sex is a PART of a truly balanced and committed relationship (true, a nice part, but still just a part). It is the final level of communication which is why it should come last, after all the other levels have been developed.
As any married couple can tell you, sexual dysfunction is generally indicative of a dysfunction in some other part of the relationship. I believe that same is true here.
Sex is an experience of giving to your partner.
This girl seems to have very little interest in you in regards to sex. She seems to be primarily concerned with her own physical pleasure as if this were some sort of training program that you were about to fail out of.
Sex is not an Olympic event, it is an expression of love and devotion to your spouse. Truly giving lovers sometimes do "things" that are pleasurable only for their spouse, and they don't keep score.
This brings me to my second concern. You are being threatened. "If you don't perform sexually up to some (unknown) level, I will go elsewhere for pleasure." Is what she is essentially saying. Where are you in this arrangement? In what way is she demonstrating her love and commitment to you?
Here is another thing which concerns me about the relationship you describe:
She says that she isn't over her last boyfriend, who she broke up with the week before we started dating, and that she wants to make sure of the guy this time.
Did they also break up because he was insufficient sexually?
She has been seeing a guy she was formerly engaged to, the only reason she dates him is because he just broke up with his girlfriend and my girlfriend felt sorry for him. This has been going on for about 1 month. She tells me that she isn't going to have sex with anyone else, and I believe her.
You are Naive
The fact that you are willing to believe her is indicative of your trusting nature. However, that trust may be misplaced. She has already shown you that sexual pleasure is more important to her than you as a person or your feelings of comfort in the relationship. She has also essentially threatened you with finding a replacement.
We do not see her saying that she wants to date other people because she feels that this is not the best partnership or because she thinks that you two are incompatible and she wants to look for someone with whom she can share a deeper bond.
No. She wants to date other people because she wants better sex!
Of course she is going to have sex with whomever she meets. Sex is a prime priority to this girl.
No, I won't give you advice on sexual instruction manuals. My advice is to carefully consider this relationship and its value to you. You said that you want to do what is best for both of you. I wonder if you care about yourself and this girl enough to end this relationship.
That may very well be what is best for both of you.