The course of platonic love is never smooth. Many people believe that there is no such thing as platonic love at all--that men and women cannot be "just friends. Be it a mental or intellectual connection or plain old chemistry, many men and women that are "only friends" end up as more. Learn how to tell your male friend you're in love with him, especially if he thinks of you as just a friend.
Pay attention to your guy friend. If you undoubtedly love him, it's best to be honest with your feelings. However, if you know he has a girlfriend or is married, it's best to keep your true feelings to yourself. Before you confess your love to him, know when and when not to do so.
By letting him know you have feelings for him, you may end up scaring him off or changing the whole dynamic of the relationship. Be sure he isn't getting over an ex-girlfriend or isn't interested in another woman.
The easier it is to be with a man, the closer you will be to declaring your love for him. Talk to his friends. Find out how he feels about you, that is, if he feels any way about you. He may view you as a little sister or a close friend who happens to be a woman. Don't exaggerate his patting you on the knee. Don't jump to conclusions. It's fine to speak to his friends, but never look needy or clingy.
Be straightforward with him. If the two of you are hanging out, let him know that you'd like to have a serious conversation with him at some point.
That way, he won't feel like you dropped a bomb on him. You don't necessarily have to "tell" him you're in love with him. Give him subtle clues. Buy him lunch, invite him to a wedding with you, go shopping with him and be his best friend.
The closer you get, the more attraction will play a role in your relationship. Be there for him. If he gets fired from his job, take him out for drinks. If his girlfriend dumps him, wallow in self-pity with him.