You two have a hard time getting matched up in terms of your energies and your emotions. When your lover is feeling tuned in and affectionate, wanting to connect on an intimate level, you're cool and aloof, emotionally unavailable. Your sexual rhythms are off, and your timing isn't the best in terms of finding times to do it when you're both revved up and ready to go.
As a result, your partner, especially, could end up feeling rejected and unloved. So why the disconnect? It isn't for lack of interest or wanting to make it work between you. Something just stands in the way of making that happen. Your own shortcomings are projected onto each other; you get mad at each other for possessing the qualities that you like least in yourselves. You may even start to represent something to each other that you don't like or respect. If you see your lover behaving irresponsibly, for example, it upsets you, because you want so much to be responsible. You could even go so far as to try to force them to behave how you want them to -- but that doesn't work. They just rebel against the attempts to control them, which could lead to indiscriminate behavior in the name of pure rebellion, which, of course, doesn't solve anything. At base, you're afraid of being rejected and your partner is scared of being repressed -- both of which feel terrible. You have to struggle to learn to let each other be the people you are.