why we are like this?!

i have seen my cousin enjoying the feel of balloon in her genitals.she too has made me practice the same. but i have the fear of balloon getting popped, but she does not have anything of that sort, she rides bike, bicycle and do almost every thing with balloon in her. she stays with it for hours together. to your notice i am a male. i also enjoy it but fear gains over as time passes. i stay with only for 3 to 15 mins. but she motivates me to keep for more time but i give up. is this anything to do with sex. but she never discloses how she manages. i need some advice on this.Does the female body differ from male body in any of the biological manner to sustain this type of fetish things?
I and her keep the balloon in bums touching anal spot and our genital spot. she has not shown her bums. but taught me how to do it. ( i went naked before her).i and her enjoy the feel of balloon in our bums, for her it is her clitoris, for me it is anal spot. we blow the balloon to its medium size that fits our bum size then put on our usual dress and do regular work. main thing for consideration is that she holds balloon for a quite a long time even till it bursts as she sits. but i feel aroused within just 3 to 15 minutes to the maximum and my penis becomes visible through the dress. she spoke to me about keeping balloon that it is a real pleasure without having to lose my sperm content. i asked her do for herself (watch cousin keep balloon in her bums) but she came forward and taught me ( she touched my bums) she never lets me watch her doing it. Is keeping balloons in such sexual areas will have any impact on physical health? I like that but, doing such sexual activities with a female makes me worried as she is elder as well as i feel i am breaking my respectable relationship with her. friends, please help in this regard. bad absurd comments regretted.