Pkaos, consider everything Zoebess said above to you, it's all true! Your girlfriend is a major red flag.....and you? What...a guy who is willing to find out what can make his partner happy and fulfilled?? Someone grab this guy quickly, please. You're a rare jewel.
Too bad that your dream of having just one woman didn't pan out. It's still a good idea these days to wait a good while before you jump to intimacy, but in this case, this young lady sounds like she has a lot of sexual hang-ups, beside being impatient and demanding. These are traits that will carry out way further than the bedroom and will increase over time. As we say in New York; "fawgettaboutit" !!
Your problems sound like a matter of nervousness and anxiety performance, all which can be resolved with time and a more understanding and loving partner. ('penetration only, is she outta her mind??)
Don't let the popular notion that being 25 and inexperienced makes you some kind of weirdo. Just be yourself and honor your own choices, and remember......there's alot of fish in the sea.....don't settle for a flounder.