My s/o can't cum

So we have sex like four to six days a week an he can last for about 30 minutes then he goes soft an wants me to suck him him off an I tell him I will but I want his cum in me not my mouth an he says it turns him off but as soon as my fertile window is over he cums within 30 minutes I tell him don't think about it but he says he feels under pressure after my period an there's no way hiding me on my cycle any ideas ladies