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The female end of the plastic connector(the end with the long part of the hose on it, has a collar on it on the very end that pushes back towards the female connector. It works like a Chinese finger trap, the harder you try and pull it apart the tighter it gets.
To relieve the tension of the clip push the two ends together then push that collar towards the female end. That should release it and it will come right off. http://www.pricepfister.com/www/ImageAssets/mirror/model/kitchen/marielle/marf532-70/28031-0600.pdf That is the installation instructions of the faucet originally. Step 12 helps to illustrate this.
The collar is on the female end. You have to push the collar back into the female end. Its usually stiff but it does go back in. You have to keep in pushed all the way back into the female end and then pull it apart while you have the collar pushed in.
I know exactly what the problem is, let me try to use the user instruction manual to try and make this clearer. It's really hard to try and convey something over the internet, but I will give it another shot. http://www.pricepfister.com/www/ImageAssets/mirror/model/kitchen/marielle/mar026-4n/26548-0500.pdf
Look at picture # XXXXX now you want to take the fitting numbered 14A the piece on the very left of that connector is the collar I am talking about. That needs to be pushed towards the right(the same way it would have to be removed)
If you look really closely at piece 14A on the drawing the piece on the very left and the rest of the connector are slightly separated. That space needs to be taken up and the fitting on the left needs to be pushed as far right as it goes. Looking at the picture where 14A goes into 14B you would have to push that entire fitting in the direction the picture indicates and push that collar the piece that would be closest to 14B in the opposite direction.
When you have the collar piece pushed in as far as it can go, while moving the rest of the connector the direction indicated in the drawing, while still holding the collar in place you should be able to remove the hose.
I hope this helps, If not I will be happy to Opt out, and let another expert try and explain it better. As I stated previously it is really hard to explain certain things over the internet and I appreciate your patience.