boyfriend is scared.. faked pregnancy.

so my boyfriend and i are happily together and we do not use any form of birth control, no condoms or pulling out. he is totally chill with this and so am i, but when it comes to talking children he freaks out. his last girlfriend faked a pregnancy 6 days after he broke up with her, gaslit him and faked an abortion after he said that he would kill himself if she had the baby. ever since then he is terrified and says he never wants children. but on the contrary his actions say he doesn't mind at all. every time i act different like have cravings, fatigued, or sore breasts he immediately says i'm pregnant in a lovingly jokingly way. he agreed that if i got pregnant he would be present at all doctor visits and the ultrasound. mythinking is that maybe his mindset of children will change the minute he hears our baby's heartbeat. i've also have a history of two miscarriages and endometriosis. he knows deep down that if it came down to it and abortion would not be an option for me as the loss of my two sons broke me to pieces. how can i help him? how can i soothe his fear?