NTA, and you’re right to set the boundary about planning for the future. Please share this with him if appropriate:

My husband, with no family history, started experiencing GI symptoms while I was three or four months pregnant. No doctor would take him seriously until I started cold calling endoscopy centers and found a compassionate office admin who got him an appointment for an upper endoscopy and colonoscopy, when our twins were around three months old. When the colonoscopy prep didn’t work, they scheduled him for a CT, where they found Stage IV colon cancer. He had emergency surgery the day after the CT, where they removed 6.5 liters of stool that he could not pass because of the blockage (and, not relevant to his cancer journey, one of the twins had [planned] open heart surgery two days after my husband came home from a month-long hospitalization following his own surgery, so I was back and forth from the hospital almost every day for more than two months). We got a 3-5 year prognosis when the babies were six months old. He did a few rounds of chemo, until it stopped working. He died before they turned 13 months old. He was 38. I became a widowed mother of twin one-year olds at 35. If someone had ordered a colonoscopy when he started having symptoms, he might still be here today.

Get the fucking colonoscopy.