Does saliva can kill sperm? Does oralsex before coitus can harm my chance to conceive? Ok to do or don't?

Of course ok. Naturally, we are talking about oral sex that does not lead to ejaculation outside of the vagina. This being the case, whatever minute damaging effect that saliva can have on spermatozoa, is completely and immediately diluted through friction of the penis on the vaginal walls. Good question, but you can rest assured.