I find the whole concept of "Sin" abhorrent, the actions of a thinking person can have positive effects, negative effects or be neutral.
Arbitrarily deciding which is which regardless of consequence and calling it a sin in order to assert control by fear is a disgusting practice beloved only by cowards and bullies

Sin produces blessing! I remember all these guys on/in me saying "oh my God ".

I do not believe in sin, nor blessings; both of these words invoke a deity of some sort. I do think, however, that most believers think that something good can come from something bad. Although, in the past, and some even today, will call the child a "bastard" and/or "illegitimate;" and have, and will, treat it as being less than a child born in wedlock.

Well sex before marriage isn't a sin, so the question is null.

What sin? This is all a religious concept. I might also say I am not a fan of Saul of Tarsus but he used language to describe bow and arrow practice for his description of "sin." You shoot at a target aiming at the bullseye and do not hit it. "You have missed the mark." In this respect we can say that we all have "sinned." It does not have to do with gods necessarily. It could involve an intention or goal you have set for yourself. We all miss the mark sometimes.

Why are you babbling on about "sin" and "blessings" AS IF they are real things instead of idiotic ways to control people invented by religion?

Stop attempting to apply logic to religion. Your time would be more productively spent ripping off your own arm and repeatedly beating yourself over the head with it.

Religion is not rational

Not according to clergy.