Yep Im stupid!

I now have a girlfriend that I have been dating for 2 weeks (3 this up coming Wednesday). I do like her quite a bit, and Im fairly sure she likes me back...well she was the one who asked me out

After hearing she has recently had over 17 boyfriends herself I wasnt too sure if our relationship would last this long

(so I didnt consider the whole trans issue to be so big)...however, she is saying stuff like how I am one of the best things that has happened to her in a long time
Now Im starting to feel more and more guilty everyday

I feel like I need to be honest and tell her I was born a girl

But I dont want to be seen as ever being a girl, because it will feel awkward! I dont think she will take the news that bad, she is very understanding (and is bisexual herself) She is really pretty, and extremely cute...and seems to be popular! We hold hands often, and people always ask how old I am (assuming Im really a 12 year old or something

) She does smoke and has had sex way more than once (kinda bad

)...but has been taking things nice and slow with me...we have only ever kissed about 50 times

I dont want to break her heart...and I dont want her to later tell the entire school about my status!
I should have thought it through

Do you think it would be wisest for me to break up with her, rather than telling her the truth? I wont really have an understandable reason for doing so tho

I swear I will never date again! Im young and too dumb, any advice would be greatly appreciated. If anyone has tips on how to break up with your current girlfriend/boyfriend, that too would be useful