i agree with many of the suggestions above... first of all juz b urself.... n choose a girl for u.... get closer to her other than juz frenship stuff... but dont forget women like men who respect them... so go ahead!
Seconding Fuzzz. Plus I'd recommend checking out this website: http://www.nomoremrniceguy.com/ngs.php
I've known guys like you - always the friend, always there to help, always there to please. While it's all fine and dandy being friends with a lady, if you want to be more then hints of passion and confidence are sure lures. This is why some women appear to go for "jerks" - because jerks tended to have a lot of (misguided?) confidence that women interpret as passion, direction, leadership, etc.
If you're trying to please her all the time and not take charge of what YOU actually want, then it comes off as under-confident and unattractive. Of course there's a fine line of balancing your needs and her needs without being a jerk about it. Men who pull off this balance are real catches IMO. Good luck!
If I were to say that to a man, then I agree, chemistry is missing. Are you working out 3 times a week to make the most of your body and raise your testosterone level? That may not cause chemistry for all women, but I notice I'm not the only woman whose eyes stop on a guy of any age who has taut muscles and no belly fat.
Don't try and change yourself if people say that you are the "perfect guy", it's just that the right girl has yet to meet your or see you in that light. Give it time and I'm sure you'll meet her. I get told that I'm really sweet and that I'd be a great girlfriend, but have only been asked out twice. It's usually when you are not looking for love, that you find it. have patience. =)
You just haven't met the one that's right for you. Sometimes there's just no chemistry no matter how good a man or woman you think someone is. You can't help you who fall in love with or who you're attracted to. Don't try to change anything; if they're telling you that you're the "perfect guy" then be glad they think so and wait for the right woman to come along that notices just like you notice her. Be patient and never lose hope. It can be very frustrating, but it comes when you least expect it. Don't worry about it so much. Everything falls into place when the time is right and it's often unexpected.