Does it goes waste?

Once a woman is pregnant, she no longer ovulates because her sexual organs are dormant as the baby grows. Therefore, she will not get pregnant while being pregnant. Any sexual activity that ends with ejaculation will result in her body just absorbing the sperm. Just like all the times she had sex without getting pregnant.

Yes, it is completely safe to have sex while pregnant. Unless, of course, a high risk pregnancy has been noted by the doctor and he orders no sex is to take place. Otherwise, sexual activity will not harm the baby or the mother. During the later months and up to the delivery date, the mother may feel slightly uncomfortable and not want sex, which should be understood and respected. Some women have sex up until delivery without any discomfort.

So, have an open line of communication so that there is an understanding as to what is expected and desired.

I hope you're trolling. No you cannot impregnate someone whom is already pregnant. Sex is safe unless the doctor says otherwise

Take a basic health class

The sperm die and get absorbed into her body. Just like all the wasted sperm that didn't make it to an egg before she got pregnant. She won't get pregnant again.