Well according to some famous matchmaker from youtube people shouldn't have sex on a first date. Though of course it is difficult to resist if there is a spark and feeling you lack breath when you see the other person and extreme nervousness. I think is better to limit yourself to good kissing and hugs, but not cross the line. But in your case as you wrote yourself there was no chemistry, so it was better to take a distance and control yourself better if she couldn't control herself better. I think it happened as she didn't have sex for a long time and also because she had so many children to take care of and maybe thought she needed a man to help her in that no matter if there is chemistry or not. You write that if you didn't have sex on a first date you wouldn't have a relationship with her for 3 years. So I think people shouldn't force themselves into relationships like that. They should give it a time for feelings start blossoming and to think the second time about it. Test-drives is disrespect to a partner, if you are not sure you want to be with her till the rest of your life (better not do it) and just wanting to test what it will be, and if she gets pregnant and you are not ready to get married it will get worse. Also your goal is to find a life-long partner and not for a while. People can be bound by sex for few years, but when this feeling of something new and wonderful disappears, then what is left? Then people find out they have different views on life, interests and goals and even don't respect each other and if not sex they wouldn't be together, there is no even friendship left as there was none from the beginning, they find they are too different and don't want to do compromise and follow only their own interests, so sex on a first date may be a reason why these couples don't last long, I don't say it should be necessarily so but I think for a better future people should learn to suppress their primal instincts for a better outcome and then they won't waste time and hang with a wrong partner and at the end find the right one.