Unconditional love does not exist in the mind of a rational person. Think about what the word unconditional means. It means that there are no conditions or circumstances underwhich you do not love that person. For example, take the person you love most right now. You might even say you love them unconditionally. Suppose that, though they were once nice, good people, they start going through some sort of change. They become more drawn in, they stop talking to you, they become irritable and rude. One day, they get an axe and kill 7 people, maybe they even try to kill you, They believe this was truly the right thing to do. There is no mental illness. Do you still love them? What do you think their reaction would be if you visited them in prison (barring the death penalty) and told them that you love them just as much now as you did before they were a murderer? They might be a little dissapointed, knowing that the qualities they had before being a murderer meant exactly as much to you as afterwards, which is to say they meant nothing.
Before going further, I should define some terms:
A Defeasible Commitment is something about yourself that you value, but would give up if you had to. Something like being a good bowler, or working at the homeless shelter, or being rich. These definitly vary from person to person, but the important thing to know is that these can be sacrificed.
An identity conferring commitment is something you see as intrinsic to YOU. "I am a good father/mother/husband/wife..." is an example. Something that's important enough to you that you would be humiliated if people found out you were actually otherwise. Losing a bowling tournament, or going bankrupt? That sucks, but you aren't humiliated. Getting caught cheating with your girlfriends sister? Another story altogether.
A note on defeasible commitements. The rational reason to love someone is for their identity conferring commitments. Being a good father or caring friend. Those are why we love the people we do. If someone loved me just because I was rich, I would be pissed if I found out. This situation with your parents might be viewed the same way.
From here we can go in 2 directions, Either
A) Your parents really don't love you anymore. Their love for you was conditional on you being a JW. Which for you was defeasible. Maybe it was important to you at one point, but not so anymore. This is not the case for your parents, they see being a JW as an identity conferring commitment, and you have humiliated them by disassociating yourself from that.
OR
B) Your parents love you. They understand that maybe you changed your mind. They love you for other, more important reasons. But, they spent how long trying to teach you what they believed is the right thing? Have you ever worked really hard on something only to have someone else wreck it? This may be what is happening to your parents. They love you, but you are shitting on their hard work. Not to mention they have to explain this to their friends.
Personnally, and I'm hoping that someone will prove me wrong, it is more likely A). This isn't entirely bad news from you. It sucks, but if they only loved you for reasons that aren't actually important to you, then you can't justify loving them back. You may say you love them because they are good parents. If they only loved you because you were a JW, and being a JW doesn't matter to you, then they weren't good parents.
This has quickly become a rant, I'm done.