Thinking to sell my hardtail.

Hi, I don't own an expensive hardtail, but it costs a lot for me—a Java Vetta with some upgraded specs. The maintenance and the amount of fixes it needs take so much from my allowance. I am only 18 with a single parent so yeah, I don't have much and the bike is costly, even though all I do is go for long rides and no trail since the frame isn't strong. I was thinking of selling it and buying a fixie instead. Then maybe buy a new MTB when I'm older and have money.

Any Advice?