Having happiness forever is a very difficult task, I won't say that it isn't possible though.  Life can throw different obstacles to you at any moment in time and it's often how we react at those moment's in time that will decide whether were happy or not.  I'm not a life teacher or philosopher and I'm definitely not an expert on the subject, but the best piece of advice I can tell you is to always surround yourself with happy people.  We tend to become a product of our own environment sometimes :)