Sometimes when you fix on a problem the answer seems as far away as Mars. Similar problems can happen with sex, when a woman fails to conceive and then goes through all manner of tests etc to see if there are fertility problems. Bizarrely as soon as all the tests are completed and there is nothing further to be done - and forgotten, then suddenly the woman gets pregnant. I'm sure this has a lot to do with stopping the stress and relaxing.
Ignore worrying about having a girlfriend. Just accept you will remain celibate and without a girlfriend, and that is the hand of cards life has dealt you. Completely ignore the fix on the final task (girlfriend)
Then grab life and join the gym, go jogging, go to every activity you can think of. Talk to absolutely everyone you get an opportunity to because you want to know about them and are genuinely interested. Go to every club you can think of. Find religion, keep pets, learn to sail, volunteer, walk, travel abroad, travel in the UK, go to speed dating for the experience. You are filling your time with putting yourself out there. Eventually you will find someone in and amongst who gives you a spark, returned I hope. More importantly you stand to find some genuine kind and lovely people (probably a few witches too along the way too - be warned) Everything else is just being open, honest and if someone cares for you they will be patient and allow you to explore life in the fast lane.
Don't give up - try and stay upbeat and as cheerful as you can be. You definitely won't be alone with this.
Never give up hope until you are at least ninety nine.