A car dealership is not the only place you can find used things. People are used everyday more times than not by people that they love and care about. What frustrates the situation is the common goal you once had is not common anymore. You are going separate directions but life tends to bring you back to a cycle or usury.
In most relationships sex is huge part of making the train stay on the track. It can get really weird if the only basis for staying together is sex. You can feel used. No matter how you explain it; you are being used because you are not agreeing to a relationship where sex is the only common goal for staying together. The poison that oozes it way into a relationship is the fact someone has changed the rules and nobody has cosigned on the investment. Love is not all used up. If indeed the ramification of why you have joined together has changed vocalize it with your husband or wife.