stage 4-new spots/chemo long-term?

Six years ago, my dad had colon cancer (stage 3) and went through chemo for six months (12 treatments). While difficult at the time as it was new, I thought it was a chapter in my past. Over a month ago, a year from his 5 year year remission, he went in to his general doctor for a regular checkup and a routine blood test. The blood test revealed that a higher level (cae?) and my dad knew right away that something wasn't right. While the general doctor wasn't sure at the time, due to my dad's history had another blood test done to double check. At this time the oncologist was also informed just to stay in the loop.

The test confirmed it was not a false positive and a CT scan would be ordered. It took a about a week for the scan to be done and another few days before we found out the results. The scan showed two small nodules in the left lung and a PET scan would be needed as a precaution. This scan again took another week and it was very daunting for myself. At this point he met with a surgeon for the lung to see what the process would be and his options. We found out a small portion of the lung will be taken out as a best measure. The other scan revealed a small spot on the other lung which has now prompted chemo after surgery (after few weeks recovery) for a few months. While my dad is happy to at least have a plan in place before surgery for after surgery, it has been very difficult for me to process. I have cried many times many nights since the news of the cancer being there again. The doctors believe the spots in the lung were probably there since last time, but they just weren't big enough on scans until now. It has been most difficult when I am by myself or don't have something to keep me busy.

I am also in graduate school and no longer live at home which were not the case when he had cancer the first time. It has been difficult of continuing my schedule and my coursework, but I have a very supportive school and professor. I believe I can finish the quarter without issue, but I felt the need to talk to my professor because I had a moment that everything felt like too much. He reassured me that he will work with me. I have had moments of thinking worst case scenario for my dad, not thinking he can't beat it or beat it this time, but is this is what is going to kill him? I don't want him to die but it's felt extremely different this time around for myself personally. I've noticed at times my breathing feels like deep breaths (not pacing or out of breath). My dad has his surgery next week. They will start the chemo a few weeks after surgery and will work around our family vacation later in the year. 

update:
After completing his chemo earlier this summer, it was determined he would need radiation to get rid of the remaining cells. He just got new scans and there are two new spots one on each of the lungs. One is 10 and the other is 3mm. There is also some possible scar tissue I’ve been told that if it is it will go away. He is meeting with the surgeon this week to see what the options are, but it may include chemo. It may include new chemo including a combo of infusion and oral drugs. He is optimistic about what his oncologist had to say, but I’m still very worried and cautious. I hope whatever happens he has a healthy journey. It’s scary to not know the unknown but I hope to have answers soon.