They possibly could have just figured that by now you would already know. I would try telling this person I love them and see if they say it back. If they don't tell you they love you you might have to talk to them.
More than likely their feelings for you have changed. If they truly love you then it doesnt matter how long you've been together your more than happy to say it reguardless of any situation. So be sure that they are not saying it back on purpose and it wasn't just a one time thing. Otherwise, I'm sorry for whats about to come next.