Figure out what your BMR is. There are lots of websites which will do the calculations for you.
Then work out how much weight you would like to lose, and a realistic time frame for doing so. So if you want to lose a pound a week, you have to eat 500 less calories than you need a day. But if you are happy to take your time, then you only need to cut 250 calories from your BMR to lose 0.5 pounds a week. That might be more realistic for you if you are new to dieting.
On the motivation front, I'm afraid that's something that noone but you can help with. If you can't help but eat sweets, then don't buy them. If your partner buys them, tell him he needs to start keeping them somewhere that you don't know about, or at work where you can't get to them.
Look at the food you eat, and work out if it's good quality food. Shift work can be an absolute bitch because you don't get a chance to snack (even very healthily) between meals, so hunger can be a pain. You need to start eating healthy but satisfying meals. If that means having to make lunch the night before and bring it to work with you then do it.
If there's any way that you can't start taking control of the food shop, then do it, and just don't buy the crappy pizzas and whatnot.
Some people use websites where you track everything you eat, and it gives you the calories for those foods. It might be a bit of an eye opener for you.
Cutting alcohol intake is one of the easiest ways of cutting calories. A small glass of wine has nearly 100 calories in it.
Why were you eating sweets at work? If you've got access to the supermarket then try eating a small banana instead of chocolate. It will be more filling, keep you full for longer, and is obviously much lower in fat and calories.
You could also try keeping an apple of pear spare, so you have something to eat directly after your shift finishes, so you don't have to endure the full hunger until you get home, and are therefore less inclined to stuff yourself