I think the most important thing you should realize is that weight loss, especially for the amount you're probably looking at (I was in your position about 5 years ago), is a process. It's not something that you can simply decide "I'm going to be healthy now" and then you magically get into shape when you want.
You've probably heard the saying "Money doesn't make the man, the man makes the money". Well, the same principals apply to fitness. You will never keep your weight off until you've changed who you are and how you think about your fitness. We've all heard that weightloss is a lifestyle change, but not as many of us realize that your lifestyle is a reflection of who you are, and that in order to change your lifestyle, you have to be willing to work to change yourself.
It's easy to spend 5 minutes introducing yourself on a forum saying that you want to lose weight. Spending an hour every day doing exhausting exercise is a whole other challenge.
Ultimately, your success depends on you, and only you. We can offer support, we can offer advice, but ultimately, you're going to have to be the one left covered in sweat and out of breath.
Your body adapts to its lifestyle. It grows to meet the demands of its owner. You demands have probably been somewhere along the lines of "process large amounts of food, and don't move much". As a result your stomach will have adapted to hold more, it's also probable that your lungs and heart have grown to a larger than average size to compensate for the volume of your body. Your muscles will be weaker and stiffer, and your body will be less accustomed to withstanding and repairing damage. Most importantly, your brain has adapted to your body size. Hormone changes and neurochemistry are all going to be tempting you back into your old ways.
I'm not trying to discourage you, I just think that you should be prepared for what to expect, and that you should know that the rough patches you run into along the way may be hard, but if you just keep doing what you're doing and adapting yourself to those new demands, then eventually it will seem as natural to you as any athlete and you wont have those rough patches.
After losing close to 100lbs, I can say that being overweight is like being physically ill 24/7. Any life you have now will improve 10-fold once you've lost that weight. Even little things you never expected to change. Your mood, your philosophies, your outlooks and perspectives, your values, and you may even find a new limit to how much you're able to enjoy yourself.
I'm quite certain that this will be one of the most significant life changes you ever make, and that once you achieve your weight you'll feel so much better in every aspect, you'll wonder how you ever managed at your old weight for that long.
Being single isn't just a side effect of your weight remember. While I'll admit that it does (unfortunately) impact how people respond to you greatly, there are other aspects that people look for. Furthermore you have to be putting yourself in the right places at the right times to meet people. While losing weight will probably help you to meet someone, you have to wonder what type of person would only meet you if you were thin.
If you're having difficulties now, it could just be the places you're going to. Consider taking up hobbies to learn a new skill. Sign up for a class where you can meet people also learning these skills and establish initial common ground around that. Once you've lost weight, you may also find new interests you would have been apprehensive about pursuing, giving you a much broader field of options to work with. You may not be aware of this, but subconsciously your personality is responding to your weight. You may not be as outgoing, you may not be able to let loose as easily, and your body language may be focusing on hiding your weight rather than social expression and communication of interest. This will also affect how people are going to respond to you. This isn't a definite occurence for overweight people, it depends how self conscious you are I guess. I'm just saying, just because you're single, don't think it's because you're ugly or anything like that, there's many factors which can contribute to it, and they aren't necessarily voluntary or at fault of your own.
Having the sense and willpower to overthrow your habits and lose your weight shows a lot of good qualities in who you are that I'm sure many men would take notice of. I think the least attractive thing a person can do is sit back as a victim of their weight and simply resolve "it's who I am, I know I'm too stubborn to change my ways, I like food too much. I was just meant to be fat". Whether you successfully lose this weight on this try or not, the important thing is that you recognized how much it was hurting your life, and you made the attempt to fix it. Even if it doesn't work this time, you'll have the experience, and you'll have the right mindset to take it that much more seriously and work that much harder at it again. Remember, if you fail, or slip up, it's not your fault, it's just your body trying to maintain the lifestyle that kept it alive all that time. The only way to defeat this is to keep forcing a change.
Just like quitting cigarettes. You didn't lose the cravings because you decided to quit, you lose the cravings because you resisted the cravings long enough to give your body time to adapt back to working normally without the nicotine.