Conceiving after cancer

My boyfriend went through leukemia twice. They did not tell him to bank any sperm at the time and he went through chemo and radiation twice. After it was all said and done, they said they should have had him bank some sperm. Does anyone have any experience with your man going through something similar? All of his doctors told us to try for a year and then to get him tested. We've been trying for about 6 months and haven't had any luck. 😔