bs, I think you should work on your social skills regardless of whether or not you want to date this girl. You can't spend your life being afraid to talk to women! Each time you go out to something social, make a point to get to start talking to a girl who you don't know. Just like anything else, the more you practice, the easier it will get.
Anyway, I caution you to not tell her how you feel because she'll think you're nutty.
1. you can't love someone you don't know. If she's aware of this fact, you'll seem emotionally immature. What you feel for her is infatuation. Love is something far less nerve-wracking which comes as you get to know someone properly.
2. most girls are (rightfully) wary of men who don't know them but confess feelings. It's too much, too soon. Asking a girl out for coffee and getting to know her slowly is a far better proposition than confessing to feelings.
3. she's got a boyfriend. So if you do tell her how you feel, the only appropriate response she can give is to start avoiding you out of respect for her boyfriend.
Please show some respect for her relationship. Don't approach her. Don't get a friend to approach her. Accept that she's taken.
But do go and start getting to know other girls and practice your social skills.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.