Pessimistic SO

We've been trying to have a baby for over two years. I've had 2 miscarriages during that time. We recently found out my body is working against me sustaining a pregnancy. (Hypothyroid, MFTHR, low progesterone). I'm on medication and I'm feeling optimistic as is my doctor. My SO, not so much. He's basically given up and resigned himself to thinking he'll never be a father. (I have a son from a previous marriage). It's getting to the point where I feel like giving up. His negativity or realism as he calls it is totally bringing me down. He's currently out of town. I'm going into my fertile days so was going to join him, now I'm wondering if I should bother. Guess I could just use some words of encouragement and advice on how to get him to be more positive.