problems BDing

so my SO and i have been together 10 years & ttc #1
​our whole time together had no problems in that department but now we are ttc he is struggling to perform.
​ive told him not to get stressed about it (even tho todays my most fertile day & im internally cursing him) if i let him kno im upset i know it will just make things worse. 
​any tips or words of wisdom?