i had a cold sore under my lips.my first time getting a cold sore and it happened when i start kissing my gf .?

Cold sores are caused by the oral herpes virus but it's nothing to be scared of. All it does is cause Cold sores or fever blisters on or around the lips.
While you have any signs of a visible cold sore you are very contagious and you can pass it if you kiss some one while you have a cold sore. Oral herpes is less likely to be passed when you don't have any signs or symptoms of a cold sore. It's safer to kiss her when you don't have a cold sore.
Get some abreva or over the counter cold sore cream to help heal the sore faster.

2

1

I think there is a possibility that you may have them. You could have contracted them from your girlfriend when kissing, if she has it. You should really talk to her about it, it it a very difficult topic to discuss, but it must be done. Lots of people have herpes simplex virus their whole life, without even knowing. It can remain dormant in your body your whole life, until something triggers it. You both should get tested. You cannot completely rely on a test that comes back negative, these tests can be false on many occasions. You should go when, and if you have another breakout, so they can swab the area and test it. Oral herpes can cause genital herpes, by performing oral sex with an outbreak. More than 80 percent of adults have oral herpes, it is very common, so dont feel singled out at all. I hope the best you are both clean, most people live normal lives, but others can get depressed ect. They say there is no cure, but I was online looking up if drake had herpes and saw this book, it costs like 30 dollars, but anyway it has the cure. It is called the one minute herpes cure, here is the link below. Hope this answer helps:)