Boyfriend and girl friend

My boyfriend goes out to do more fun activities with one female friend he lives with while he never is interested in doing fun things together with me anymore. We only ever seem to do mundane things together now like do homework or grab a quick bite to eat or watch television at his house. If I initiate a plan, he always hesitant to commit. He says he loves me a lot and I'm certain he's faithful, but what is going on??