Why sometimes love makes you quit smoking?

The person is a smoker and abuser, just like the world around him. Not too like a bad person but not so very kind.
Then when he fall in love for someone and try to be with the girl he want to be. He just feels that he just start to make changes in himself he doesn't know why and how it happens but now his happiness are slowly-slowly going to bound with her. He started exercise, taking care of himself, quit abusing and smoking. And try to change utmost in hope that she will like him.
But why all this things happen? He can't control himself by self instituituon and will power but the feelings for someone makes him to do this things so easily. I think the love that grow in himself gives him that power. And how this happens I just have some views.

The emotional reason
When we fall for someone we want to get her so eagerly that we can do whatever she want we doesn't want to make a bad impression on her so that she take as just like the others, but if we are the same person how could she ever think about us.
We try to become not like she wanted but we not know that yet. But try to prepare to so good so decent guy so that it took hard for her to reject ourself from her heart.
And the will power to change is never comes from self introspection because if we quit smoke or health so that we live something longer it's doesn't feel like winning or being happy by living longer for our mind but when its same thing just stick with our love our emotion that we see things like quitting things makes us good person and takes us close to someone makes the situation win win for us. That love drive us the will power,the potential to ourself that promises with ourself can't get to us.

The scientific reason
Science show that when we get attracted to a person dopamine releases in our brain, increase serotonin levels and which produce oxytocin hormone so called love hormone.
Whereas the other side, Nicotin present in cigrattes gets into our body activates structures present in your brain called receptors. When these receptors activates releases dopamine that makes your feel good which leads to realease oxytocin in some amount.
So just like we know love is also a play with science and we see that even exercising, eating favourite food and chocolates makes you feel good because of that. And that's the reason we can more easily quit smoking when we are in love because in some sense we are looking for the same harmone in both scences to makes us feel good and makes happy.

But love is not only about some science stuff or facts. Love is love. And we know that human nature is to make ourself happy and when we are going to like someone we want them happy whoever they are friends, family or someone special and quitting smoking and abusing is just a small effort we do to makes him happy and by doing so we understand that we are truly in that person and if we do that things that even our will power can't do that means the person is really really special and there is no doubt about that.