Just or unjust jealousy?
So, you have your friend and you spend time together and you have fun together and you see nothing wrong in such a friendship. You don't care about what people say or about what they think, you know the truth and this is the most important thing. You know you are friends and you won't lose your friend because of other people's misunderstanding.
Though, no matter you are a man or a woman you will soon face the necessity to make your choice between your friend and a one you are in love with. It is common for those you are in love with to be jealous about your friend and your friendship. Sure, you can say that if he or she loves you he or she has to understand you, though don't rush to make your conclusions.
In most cases the jealousy people reveal is a just jealousy. They do have reasons for being jealous as they are not as blind as you are and so they see a bit more, they see all those looks and hear all those tones of voice you can't see or hear because you are blind with your faith in sacred friendship between you and your friend.
Indeed, it is the just jealous they have and so there is no point in blaming one that he is too jealous of mad. There is a point in taking a good look to your friend and to behavior of your friend. Try to analyze everything and then you may see those things you weren't able to see yet. Don't mass with the one you in love with, think over.