I mean it. When you fall for someone your brain releases dopamine (among other chemicals) which is the same chemical that is released when someone takes cocaine. We are thought to be wired this way in order to get us 'hooked' on our new mate and feel so crappy when we are not with them (due to a drop in serotonin) that we keep seeking them out...survival of the species and all.
The problem comes when you are 'hooked' on someone and that someone is not 'hooked' on you. Or, they are 'hooked' but are unavailable for a relationship (married, interstate, workaholic, addict..or someone who just doesn't have what it takes to form a healthy stable relationship).
Emotional reasoning is where we use our feelings to determine what is 'true.' When we get hooked on someone, we use our intense feelings for them to convince ourselves to disregard reality and believe that they are "the one", our "soulmate", it is "meant to be" and that we won't ever feel like this about anyone else (also known as overgeneralisation). It is the combo of the intense feelings of love highs and come downs/withdrawals, plus these unhelpful thinking styles that make people stay hung up on someone far longer than is sensible.
There are also certain types of relationship behaviours which are likely to perpetuate the addiction.
Intermittent reinforcement refers to a process by which behaviours are rewarded (i.e. you get what you want) part of the time. Scientific studies have found that if you learned that getting what you wanted was unpredictable, even when the rewards stop completely, you tend to keep engaging in that behaviour for longer then if you had previously gotten what you wanted every time.
Think about a pokie machine: the pokie machine pays out only occasionally, however, gamblers will keep feeding money into it for a long time in the hope it will pay out again. If the pokie machine was set to pay every time, and then stopped paying all of a sudden, the gamblers who had previously been using it would give up more quickly.
This means you are likely to remain addicted to someone who was not 100% there when you were dating. A date who was responsive and reliable is not as likely to elicit as long of a withdrawal as someone who was ambivalent - who would only occasionally be available and responsive and at other times would turn away or turn against you.
So what do you do if you are unhelpfully addicted?
Try to eliminate all contact for the time being. Having another 'hit' of your favourite drug will just lead to the same old come down and withdrawal the next day/week.
When you get the urge to look him up or contact him/her:
Remind yourself that your brain is just in withdrawal and the feelings will pass
Have a list ready to look at of all the reasons the relationship didn't work out and another of all the things you are looking for in a relationship
Remind yourself that in these situations decisions should be made on the outcomes that you want, rather then how you feel (because your brain is on drugs at the moment...see point 1)
Act compassionately and lovingly towards yourself. Be gentle, don't get mad with your urges or your feelings, they are natural. Be loving, remind yourself that you are worth a relationship with someone who is able to love you in the way you want to be loved.
Get distracted. Call a friend, watch a movie, go for a run...the busier you get at that time, the less you'll notice the uncomfortable feelings of withdrawal and the less you'll be prone to giving into the urge for contact.
When will I know I am not addicted anymore?
There is no real rule of thumb here. Essentially, you know you are over it when you can see him/her and not feel much and also don't have the urge to contact him/her when you part again. This often happens when you are in love with someone else. However, it can also happen if enough time has passed that you are no longer hopeful things will work out or viewing anything he does as a genuine sign that it could work.