My wife felt the same way when I first came out to her. She was worried about what other people would think. The answer is that most people who care about you two won't care about you being trans as long as they see both of you are happy. That's the important part.
Second. Not transitioning for someone is sort of like dropping out of college to be with your boyfriend/girlfriend/SO. Or like not taking a good job so you can be with that person.
One important thing is that you're out, and there's no way to put that cat back into the bag. Sometimes being trans is enough to make someone leave, transitioning might not matter much one way or the other. Sometimes, going slow (really slow) can help, or going to therapy together can help. If you are transitioning with a partner, then remember that your partner must transition, too. They haven't been dealing with your issues for however many years, so this all new to them and they need time to adjust.
Lastly, if you do decide to not transition so you can stay with her, you should know that being trans doesn't go away. A lot of us can testify to the naivete of thinking we'd be cured when we got girlfriends, or got married, or fell in love. The way you are is the way you are. You can suppress it, and try to forget about it, but a lot of trans people find that it's a recipe for a lot of unhappiness. Many of them end up transitioning anyway, it just ends up happening a lot later in life.
I think therapy is probably a good idea for you at least, and maybe for both of you. Everyone here will lend an ear, and give you their two cents, but the opinion and advice of a good professional is (usually at least) worth the price of admission.
