Today is the day that you stop defining yourself as a guy with low self-esteem. That label isn't helpful, and it's going to hold you back if you let it stick.
Next, think about something that you're good at. How good are you? Whatever the answer is, spend some time getting even better, so you have something to be proud about.
Take on something new, and work on that, too. Maybe learn another language, or ballroom dancing, or how to work on cars. It doesn't matter what it is, just take on something new that's outside your normal comfort zone, and work on it. It will be uncomfortable at first, but you will be learning alongside other people who will also be struggling. As you get better, you will feel better about yourself.
Do some volunteer work. You're not getting paid for it, so you will probably get praise and thanks just for showing up, and any fair effort after that is great. You will feel great about yourself after doing some volunteer work.
Finally, get more exercise. It's a good way to cope with stress, and as you get more physically fit, you will have something else to feel good about. Women will find you more attractive, and you will be healthier.
I realize that these are some time-consuming suggestions, but they will get you out of the house more, and you will soon be too busy to feel down about yourself. At some point, you will look in the mirror and realize that you're a more confident and successful guy. Also, if you have all these activities, you will have less time to obsess over your internet crush, and when she finally meets you after moving to the UK, she will be more likely to be impressed with you. If things work out between you two, you can always cut back on the other activities. Keep an open mind, and you might just meet somebody else, maybe in a classroom, or maybe doing volunteer work or exercise. The possibilities are endless and exciting, don't let them narrow down to the opinion of one person you met over the internet.
Good decisions come from experience. Experience comes from bad decisions.