I was in a similar situation to you when I was 18. Never had interest from women, very shy, loner, not a lot of friends. By the time I had turned 19, a lot had changed. I had lost some weight but overall I looked pretty much the same. There was only one difference about me overall: confidence. I basically forced myself into situations that used to make me feel uncomfortable. Suddenly, I found myself happier, more comfortable in my own skin, more able to meet people, getting interest from girls.

You're a decent looking guy (plus you play runescape which instantly makes me like you), you have so much potential overall. You seem pretty self aware as well which is a huge deal for someone at your age. All you have to do is step out of your comfort zone and you will start making progress faster than you think. Be yourself but be the best version of yourself. If you want to get in better shape, join a gym and eat better. If you want to make friends, join a club or something like that to meet people of similar interests. If you want to be more attractive to girls, know what your strengths are and own them. The power is all with you friend, and I believe you can do anything you set your heart and mind to.