trans boyfriend

me and my boyfriend have been dating for a little over a year now and he recently came out as trans and will start taking estrogen next month. I myself am bi and don't mind it but one thing bothers me, I will never be able to have biological children with him. after he is on estrogen he will stop producing sperm and even if he stops taking the meds he will never produce sperm again. I am ok with adopting I just wish we could have a biological child