Dear sir
Iam 17yrs young boy.I study in 11th grade science stream in college.I think that I would never have love in my life but I was wrong I completely lost my heart to my special my love.I love her very much even more than my life but the problem is that she has another boyfriend .I already know that she has boyfriend but I can't forget her.I tries many times convincing my heart that she have another boyfriend but I lose.my heart won.so,I want her.I make plan to give her my first time loveletter in upcoming valentine day i.e. feb14th.Is it good time to give her.I heard that her boyfriend is fighting types boy but amn't afraid I love her very much.we had sometimes good talk in outside the college.I many times message her with my mobile but she didn't reply.so what should I do to spend my whole life with her happily.it's my first love so please give suitable answer which I can do .

Well if she isn't replying, then my dear, she may not be that into you!

Especially if she has a boyfriend.
Do you think you LOVE her or you are infatuated by her?
If you can't live with out her knowing how you feel, then you can always take the risk of delivering this letter, but you must be aware of the reprecussions behind that (her boyfriend getting upset and violent).
There are other subtle ways of letting her know you care. Maybe start by telling her you value her friendship, and see if you can live with just being friends. If you tell her how you feel, and she does not feel the same way, you will need toback off, and not "pester" her with advances and love letters.