>>5 This.
and
>>7 This.
I don't think the sex must be involved in a relationship - But its become "declassified", if you will. Some time back in history, and to specific cultures now, sex was a very 'forbidden fruit' kind of thing. You can do this only when married, you can do this only with who you love, etc.
These days this is not true. It is a biological function and it is more or less treated as such. Relationships don't
require sex, but neither do they restrict its presence. It happens no sooner, and no later, than both parties are ready.
"but I wasn't ready and gave in anyway!"
The above is a common statement, but my answer is really that its entirely their fault. When you give your consent, reluctant or not, you have agreed. If you don't agree, then you don't give your consent. Peer pressure? guilt? What do those matter in the face of your own integrity? Further more the backlash from realizing afterwards you regret your actions is worse than the temporary hazing you might get for saying 'no' in the first place.
Of course, things like rape - where consent is not given - are still illegal.
So now sex only happens when we want it. You could ask a similar question of "why is sex happening so young now?" - The age of consent has changed, both over time and over place. It used to be as young as 13-14 in some places, and in others remains a very strict 18-20.
Depending on how far back into history you go, pedophilia didn't exist. If both sides gave consent, it was a go - No age involved. Different times, different cultures. There's no ground to properly stand on to say one was better or worse, considering they both prospered in their own way.
If anything, I think we're beginning to move somewhat backwards in time. Sex began as an unrestricted biological process that only required consent - Then became a sacred thing. Put on a pedestal, and restricted vigorously for only special occasions under specific restrictions. Now those conditions are being loosened. We're moving back to it just being a biological thing.