Feel like it's pointless

Why do I even bother showing up for work, when my co-worker constantly takes off. I work for the city in the transportation department as a bus aid. It's ok pay, I'm an aid that helps tie down wheelchairs and help get the other special needs children in and off the bus. I like my job because I love working with children. I'm working towards becoming a speech pathologist for children, it's a step forward toward where I want to be. Anyways, so yeah!!! My coworker has been calling out on the craziest stuff from keys gone missing, locking his keys in the vehicle to I don't feel like coming into work. It doesn't loik hood to me that it's so slack and they don't ecen care. I've been at my job for 6years and accumulated 3months work of sick snd personal time, that I haven't used yet. The only day I don't work is my bday. I missed so much work because of him. Since I've had this job, I've been trying to get out of and into another job, but no luck I'm still here 5 years later. (the runs would be split up, yeah if he doesn't work and my job doesn't have anywhere to put me then, there's no work for me, it gets irritating; I've tried to speak with my supervisor, but thet won't do anything about the situation)