Sleeping with a partner can improve the quality of your sleep. A recent German study, published in the Frontiers in Psychiatry found that REM sleep increased in duration and was less likely to be disrupted when couples slept together when compared to when they slept by themselves. They were likely also to synchronize their sleep patterns when sleeping together despite the possibility that they may disturb each other. 
For the study, the research team picked 12 young, healthy, heterosexual couples. The couples spent four nights in a sleep laboratory where the research was carried out. The couples followed two sleeping arrangements co-sleep and individual sleep and various sleep parameters were assessed during this time. The couples also had to fill up a questionnaire on their relationship. These were designed to gauge the duration, depth, and passion in the relationship.
The team found that when compared to sleeping individually, co-sleeping was likely to increase the likelihood of REM sleep by 10 percent. It was less disrupted with more limb movement. REM sleep is associated with memory consolidation, emotion regulation, creative problem solving, and social interaction. The team also found that when co-sleeping, the couple were more likely to synchronize their sleep. Significantly, there was a strong link between the synchronization of their sleep patterns and the depth of the relationship.