I have two equations which describe the Love of Romeo for Juliet (R) and Love of Juliet for Romeo (J) as a function of time, $t$.
$R=-c_1e^{3t}-c_2e^{2t}$
$J=2c_1e^{3t}+c_2e^{2t}$
They will stay together forever if $R(t) \gt 0$ and $J(t) \gt 0$, for all $t \ge 0$.
How to determine if they will stay forever or not?
Focus on the feeling, not the intensity (divide by $^{3}$), and let time pass towards eternity ($\to \infty$); or the end of it.