I graduated in May 2017; lived outside of the US for 9 months, but currently work in the US full-time, will I be able to file a k1 petition alone?

My Spanish boyfriend and I have been together for 3 years and hope to file for the K-1 visa in Feb 2019. After I graduated in May 2017, I moved to Spain and lived with him for 9 months before returning to the US to work full-time. I've read on several sites that proof of 3 years of tax returns will be required when I petition for him. I'm worried that because I will have only been working for 4 months by the time I file that I will run into problems. I currently make enough to support us both and I prefer to file without a sponser, but do you think it will be required?