any advice?

me and my boyfriend been together for a year i am TTC with him for baby #2 . Now baby #1 was from my previous relationship 3 years ago . Now my current spouse only has 1 testicle due to a surgery he had almost 2 years ago do you all think that his sperm count it low and that may be the reason why we TTC but cant ? 😪 he often feels bad because he always says its him but im not sure . Any ideas or advice?