If you tell yourself you can then you can do anything you put your mind to. Have faith in yourself. Be honest with your boyfriend, if he loves you for who you are he will except your birthmark.
I would say talk to your friends about it. The ones you feel the closest to. If they are your true friends it will not bother them.
Most of my friends when they see someone staring at me weird they are the ones that get offended. I do not even notice it any more because I am so use to it. I am in sales so I talk to hundreds of people in person a day.
Trust me when I say this I have talked to a couple people that have birthmarks that are worse then yours. I know people with 60%, 75% and 100% of their body head to toe with a birthmark. There are a couple of them on this website but I have not seen them post in a while.
Keep your head held high and do not let anybody stop you from what you want to do with your life.
Also, I do have my own website if you would like to check it out. www.hankspws.com
Talk to you later.