If you're 31 and and can't maintain a proper relationship then there's something seriously wrong with your personality or physical appearance. "Yourself" just isn't good enough.
I am not a bad looking guy yet other guys like me seem to have rich pickings.
Let's talk about your looks a bit, assuming your avatar is an image of yourself. You appear to have a receding hairline, which is a huge turn off at only 31 years old. I can't see your body, but by looking at your shoulders it looks like you're desperately in need of a gym membership. Have you been exercising daily? Even if it doesn't improve your physical appearance exercising daily will increase your testosterone levels and help improve your personality. That said, while your physical appearance seems to be significantly below average, there are no obvious defects (i.e. missing limbs, terrible teeth, morbidly obese, etc) that would prevent you from forming a romantic relationship. Physical appearance isn't very important to most women anyways. Just understand that you're not going to be the guy that gets a girl based on looks alone, and you're going to have to work harder than average to above average looking men.
They just 'friendzone' me for no particular reason. I dont consider myself boring at all.
A woman will friendzone a man when she view him as either as a gay man, an asexual man, or a woman. Something in your personality is making it so that women don't see you as a sexual, heterosexual man. You say you've tried being confident/arrogant, but you must truly
be confident (not arrogant, confident. Look up the difference). Women will be able to tell if you're faking it. Most likely the relationships you did have were because the women were initially fooled by your act, but eventually caught on that you were truly insecure inside. Additionally, the fact that you had to use online dating to meet them makes you inherently less attractive.
You need to increase your confidence level. You do this by being successful in life. Start working out daily. Make it a goal to talk to 3 new women per week. Try to improve your career. What field are you in? You are in the UK so it might be different there, but taking golf lessons has done more for my career than any degree of certification ever could.