I've taken a look at the code and I cannot fathom how this is possible to achieve in an unmodified game. I have back calculated the 'love2' scores for the secondary girls and they come out as follows.
love_ali2 = 2.6
love_jul2 = 0.6
love_rac2 = 6
love_tan2 = 2.8
total = 12
With the formulae in the game it should be impossible to get any one of these scores above 5 and the sum of them should always be 10 (+/- 0.2 with rounding).
The secondary girls are calculated by 1/2 influence from central girls + love2 index. When you spend time with a secondary girl, their love2 index is increased by (amount in 1 to 3 range):
$ love_rac2 += round((5-love_rac2)*0.1*amount,1)
The remaining score are reduced by splitting up remaining points out of 10 and splitting it amoungst the other secondary girls, in proportion with their previous score. As below for Alice.
$ love_ali2 = round((10-love_rac2)*love_ali2/(love_ali2+love_jul2+love_tan2),1)
Once again, can't fathom how this occurred. The math is a little complicated, but not that complicated.