Keeping motivated

I would challenge you to begin changing your mindset about this being a "diet" that is going to be "over" when you hit your goal, and thinking instead about "how can I make this a lifestyle?"

I agree with @Panini911 that you might reduce your rate of loss goal, which will up your calorie allotment and may make it easier for you to stay within range on a daily basis even without a lot of exercise during the winter months, and to get by with a few extra calories socializing on weekends.

Thinking in the long term, you know very well that winter comes every year. . . so with that in mind, what might you do NOW to set yourself up to continue being active in the winter far into the future? Are there different exercises you might be able to do at home when it's too cold and dark to walk (simple calesthenics? an aerobics video? jumping rope in the garage?)? Is there a community rec facility near you that you could join and get access to gym equipment or a pool for the winter months? Is it possible to add some moderate activity to your daily routine (park farther from the supermarket door, walk up the stairs at work, drink plenty of water at work so you have to get up and pee every hour or so? ). Is there a mall or other indoor facility where you could walk in the winter--maybe in the morning or on your lunch break if after work is too demotivating.

Thinking in the long term, you know your circle of friends and how you like to spend your weekends and the role that food and drink plays in your social life. So, can you put some effort into figuring out your options at your social group's regular hangouts? Can you build in a couple of calorie "save days" during the week where you can plan to be under your goal for 50-100 calories so that you can "spend" those on the weekend? (This works well for me-- I try to "bank" about 350-400 calories per weekday-- or about 75-80 per day--to "spend" on Friday or Saturday nights.) Can you eat something before you go out and/or pack some snacks for yourself so you're less stressed about choosing menu options? Can you sneak a phone picture of what you ate while you're out so you can figure out how to log it later [foodie pictures are all the rage, so your friends probably won't even notice after a while!].

While these specific suggestions may not work for you, my point is that if you start thinking about the long term, you can change your focus from "motivation" to do what you see as temporary to "adaptation" to do what you see as permanent.

Good luck to you!