I think you're not the only one who feels sad and lonely during winter...it is rather a dull season, everything is grey and cold, the lack of sunlight makes you feel tired and you're just unmotivated to come out of bed and face the cold >__<
.....odly it's my fav season lmao but I'm weird....err..anyways
Maybe you can try and make small changes so you can make winter more easy and enjoyable to go through.
I like taking walks, you can take them in the morning while the sun is still up and get some of that sunshine lol.
Chocolate makes us feel good right
? how about some nice hot coco and you can lit up that fire and watch some movies all cozy in ur sofa with blankets and cute pyjamas and...err...well..usually works for me XD
You can also exercise at home, physical actvity is important...I tend to play with my wiifit for an hour or 2 and it's a nice way to warm up ^^
And heck, if its winter and cold and utterly depressing outside, then just stay indoors and do indoor activities ..you can even embark in fun projects and make some handmade gifts to give for x-mas ^^ and try to take small steps into going outside, if you feel lonely and ur single well make it so it isn't so