I don't agree. Don't say you love her if you don't feel it. However, if you do love her,and just have trouble saying the words, find another way to tell her. Just be honest, whatever you feel. And if you truly don't have feelings for her, don't string her along. The longer this goes on, the more you will hurt her when it ends.
It is actually very wrong not to appreciate your girlfriend and express the way you feel about her for that long. Women love being appreciated and being shown love all the time. Those words in reality mean a lot to any woman or else she will shift to another person who will say them without hesitation for her.
My husband first told me he loved me 4 months into our relationship. I knew his feelings were genuine (he is so not the type to just throw the words around) and my feelings were too. We have now been married for almost 4 years and been together for almost 7. If you truly love her, tell her.
I'm assuming you're not in high school anymore, in which case saying "I love you" is a commitment. It's not just words anymore, but a significant promise. So, yeah; never say it if you don't feel it, bro. Good luck!