In Neuroscience, To get 很爱很爱 someone means you gain a complete control over his/her hormones, which are especially active in the brain's emotional center--the limbic system. And the limbic system, as one of the dominant decision makers in the brain, makes him / her to stay with you as much as possible.

But you may not get a complete control on the other major control center of the brain, the frontal cortex, the logical planning center. And frontal cortex is the most prominent one in a mature human brain. So his / her logical planning center could command him / her another way. Which could be as ^自由鸟^ said 让他/她选择自己的幸福.

To give some links on how neurosciences explain the brain and the love it generates.

http://info.med.yale.edu/chldstdy/plomdevelop/development/november.html
http://www.deathpenaltyinfo.org/article.php?scid=27&did=977