Ex- Partner

So after a well over 4 years on and off my ex and I were done but our last relationship togheter we tried getting pregnant, he came in me well over a month & eventually I got my period , (due to recent emergency surgery I had I found out I was super fertil & I already have two babies) anyways.we've stayed good long distance friends we don't see eachother but we played a big role in each other's past life so when ever he needs me for advice he knows I'm there just as he is for me but now it's been a while of him being with his new relationships and he has had no luck in having kids but he's scared to go get checked or something I think his not fertile , but I really feel bad for him, what is the first step to finding if your not fertil?