Low sperm

My fiancée is going to be 45 this year & I just turned 24 ., I love him very much he does everything for me lately we’ve been trying to have a baby & with no luck (I know things take time) but I’m trying to get him to see our doctor to see if maybe his sperm motility is slow and he argues with me about it every time he eats really unhealthy & I try to help him eat healthier I don’t bring him to the groceries with me but he still ends up eating junk ,, I myself am going to see the doctor to make sure that I’m ovulating but he just won’t do it . I don’t know what to do. Should I just leave it ? What should I do ?😫😫