I've tried different sleeping times and 7 hours seems to the one that suit me the most. Obviously this is not an exact science and I guess that as long as you have between 6 to 8 hours sleep, it's ok.

Regarding my relationship, we've got a very close one, but obviously we do thing on our side in the evening. Sometime I'll reading or gaming and she'll doing something else. But we like to keep the "going to bed together" and "having breakfast together" as much as possible. It's just more quality time added to our relationship.