Last year I met a girl and we became best friends. We talk a lot together. Lately I noticed that I kind of love her. If I don't talk to her, I get really really depressed. The problem is that I am a very shy person and have never told a girl I love her. I don't think I can tell her that I love her. It would really feel awkward and ruin our friendship, if she didn't feel the same toward me.
Another problem is that my mother once said that she was okay with us hanging out with Muslim friends, but she really opposes the idea of having a relationship with someone of another religion. This girl is Muslim.
What should I do?
While you strongly like this girl, and love being around her, still I wouldn't say that you've reach the level of love described in the Bible (I Corinthians 13:4-8). I suspect that much of what you like about her are things that you've imagined about her. When you do meet the person you want to be with the rest of your life, you'll find it much easier to tell her about your thoughts and feelings toward her.
Right now you are focused on the present and your feelings toward a girl who treats you with respect. But you also need to consider the future, which is how your mother is looking at things. Christianity and Islam are not similar or even compatible religions. While you could marry a Muslim and each of you go your separate ways when it comes to religion, what happens when you have children? Which religion will they be brought up in? The fact is that children who are raised by parents of different beliefs often grow up to become atheists because it appears to be the easiest way to deal with contradictory messages.
I would suggest continuing to be friends, but realize that this won't be something that will grow into a marriage. Keep looking for a woman you want to spend a lifetime with. Pick with care and don't give away your heart to the first woman to pays attention to you.