It's no secret that winter is a time of year when humans are mostly indoors, but there might be some good reason for this. Love is the essence of life which one can enlighten and then remain with it forever. The relation between winters with cherished romance can make anyone happy in their lives.
Let's take a look at some studies to find out why it seems like winter is full of romance.

The first study was conducted in the UK by Emanuele et al., and it looked at long-term trends in human activity across 10 countries with different climates. Their findings showed that summertime activity levels were lower than wintertime levels, and that this trend continued throughout the 20th century.
The decrease in activity in summertime may be associated with many factors, such as the fact that summertime is often associated with vacation time. The authors concluded that the findings suggest a "movement away from the land-based and farm life towards more sedentary behavior."
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A study by Lassen et al. investigated how teenage males had more partners and engaged in more promiscuous behavior during the winter than at any other time of year. In fact, there was an increase of 10% during the winter months. Authors concluded this was due to some unknown climatic factor which has effects on reproductive behavior in humans.
"In particular, people focus on direct production of goods and services for their own consumption."
Other cultures have different winter habits. In Japan, many farmers remain active at the start of winter. In China there is a tradition of going out in the snow to collect pine nuts.

The change in timing of seasonal activities may be explained by our tendency to change our work- or school schedule with increased awareness of daylight saving time (DST), which helps regulate the work-day length.
Summary: Summertime seems to lack romance, but it may simply be because of human laziness.