The simple fact that you two are in a relationship is a strong indicator that there are plenty of other positive aspects between you, because this one makes things pretty difficult when it comes to relating naturally as a couple. Your partner likely attempts to control you in a way that makes it hard to get along. You feel restricted in your affection and romantic expression toward your lover, and it could come out cold or just stilted.
Your lover tries to restrain your natural way of being in a relationship. You could feel as if any affectionate advance you make toward them is rebuffed as inappropriate in some way. Needless to say, this makes it hard during moments when losing yourselves would be appropriate -- when you're being intimate, for example, or just out and supposedly having a good time. At times, you may have even felt as if your romantic overtures were made fun of or just flat-out denied. Where does this come from? Look at the experiences you've had in your lives with all kinds of love -- relationships you've each had with your fathers, for example, or with past lovers. You may have experienced this kind of coldness and lack of affection before, and somehow, when you two got together, those old feelings from past relationships were stimulated. To keep this relationship strong, it's important that you face your problems head-on, and then get over them.