I don't know the numbers well enough to give solid advice, and the time-scale over which she doesn't want to be dumped seems relevant. One of the factors of modern culture is that young people regularly change almost all of their social set- high school students going to college, college students going into the workforce, etc. - and many relationships don't survive that transition. I don't know how to plan around that. In absence of that, I suspect the optimal strategy for life-long relationships is sexual reserve (because the costs of getting a relationship to medium-term are so high).

Actually, something even more relevant than "not getting dumped" might be "percentage of pre-menopause time spent coupled." Putting out seems like a good strategy for maximizing the second variable, or at least ensuring it doesn't get too low. I would not be surprised if the timescale necessary to find a guy willing to wait 90 days to have sex is measured in years in some milieus, and that involves a lot of guys losing interest.