Online freelancing is growing rapidly. However, despite this rapid growth, we have a limited understanding of online freelancers' long-term experiences and evolution, or how online freelancing influences freelancers' broader career goals. To address this gap, we interviewed a set of online freelancers at two time periods, two and a half years apart. We found that long-term engagement with online freelancing involves a unique set of financial, emotional, relational, and reputational burdens that represent the overhead of maintaining an online freelancing career. We found that this overhead influenced online freelancers' participation and perceptions of online freelancing over time, as well as the strategies some freelancers employed to manage their careers. Our findings further highlight how online freelance platforms can afford unique career development opportunities over a longer period of time, including career exploration and transition, entrepreneurial training and reputation, and skills transfer. Based on our findings, we present policy and design implications to increase the sustainability and accessibility of online freelancing.