Advice needed!

I'm coming up to my fertile window, so naturally I told my partner that we need to BD a fair bit next week. 
​His response....he's going to get some I'm slightly offended that he would need it, I mean he's young and surely it should be alright in that department. Maybe I'm just reading into it too much, or am I?! And the other thing is can Viagra be harmful when your TTC?!