Well yeah this can seem like a huge hurdle to overcome, and for me it definitely was, but once you're over it you'll feel WAY better. A girlfriend isn't just for the sex and stuff, shes there for the support too, and my girlfriend has been great supporting me, and understanding my problems related to gyne. I'm 20 years old, about your age, and I can say that telling my girlfriend i had boobs was one of the hardest things i'd ever done. When i look back at it, i'm glad i did.
Heres what I did.
I took her outside, to make sure we were alone and wouldn't be bothered, and I told her I really needed to talk to her about something. We sat outside for a little while small talking, as people do when they're nervous and then she asked me 'whats wrong?'. So I explained to her (after a little sidestepping mind you) the whole concept of a condition called gynecomastia and how it was something i was suffering from.
She took it well.
She told me how of course she noticed, but she just thought it was because I was a little overweight. Ever since then I've been able to talk to her about it with ease.
To all of you guys out there not telling your girlfriends, just do it. She'll notice eventually, and she should understand and be compassionate about it. If she isn't, then you really should consider the type of person you're with, and your reasons for being with them.
