Confused and not sure what to do... (should i leave her)

Hello All. Right now I'm at a crossroads in my relationship. My girlfriend and I have been together for almost four years and now I feel it's time for us to decide if we're going all the way or not - up until now we've just been drifting along. I told my Girlfriend last week that I needed some time to think, to get my head straight, so we agreed to take some time apart for me to do that - this was absolutely horrible and we were both very sad about this. So over the past week I've been thinking and I'm not sure what to do next. I've figured out what my issue is, so i'm hoping if I spill my guts out here, I may get some opinions on the best course of action. My and my GF get on famously. We're enjoy the same things (mostly) and we're always laughing. I have 100% trust with her and she is gorgeous (although has put on some weight over the past couple of years, not that I'm judging, as so have I) She is so supportive and I know she would be a loving, lifelong companion. Even after four years, we're extremely cuddly. HOWEVER, I'm plagued by doubt about the relationship and have been unable to commit to a lifelong partnership. I've managed to boil this down to one main issue: I'm now 30 and due to a birth defect and some other issues, I never experienced many women. Please don't judge me on this, but I really feel like I've missed a big part of being a man, which is the excitement of being out there dating and meeting laidies. To make matters worse, it seems that every weekend I go out I am finding girls who are automatically into me without me even doing anything. It's bizzare that this is happening now but fending off these advances is making me think - am I letting something that will only be around for a short time slip past me. Is this something I'll regret when I'm old and grey and past the stage of getting lots of attention from attractive young women? On the other hand, I know I've got a great thing with my GF for all the reasons mentioned above. Sorry if this sounds awful, I do feel terrible but its just the way I feel. I'm totally confused. I care for this girl on the deepest level and upsetting her makes me feel as bad as I can possible feel. So I welcome any thoughts or comments on this situation to hopefully somehow help me through this horrible situation. Thank you for reading.

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