The exact reasons why you decided to make this decision are not clear, but you must be careful .. This can get out of hand, can misinterpret your intentions and believe in other things more intense than just sex. Your sexual life you handle as you see fit but remember that you should not hurt others, it is not the right thing to do. If they agree that it's just sex, well, but if not, you should leave that far. These kinds of things often break good friendships by hurting succeptibilities. Good luck when you talk to them.