Hi Romanova, the issue you are referring to has nothing to do with life in a couple. Each person has his own internal clock (circadian clock) and changing it for whatever reason (spending more time together with your partner included) is difficult to do. Timed exposure to light in the morning and taking melatonin supplements can help change the timing of the circadian clock, also keeping yourself on a fixed routine of going to sleep at the same time helps. If your partner is aware that his internal clock hurts his relationship than you have nothing to worry about, just let him follow my advice or talk to a specialist and hopefully everything is going to be all right. If he doesn't want to cooperate then you two have a very different problem. Best of luck!