On cards splitting:
Like Marco, I suspect your faros. Faros should be done almost force-free. The packets should combine like a zipper, gradually interlacing from one end the other. If it it does not look like a zipper when you do it, of if you need to apply great pressure to force the packets together, something is wrong with your technique. I recommend the get The Virts' tutorial on the perfect faro if you seek a good source. You can buy the tutorial with a purchase of the ss16 deck, or you could drop them an email at support and ask to buy this tutorial specifically or the SS14 tutorial bundle, which also include Rubix opener, Strobe, Squeeze and the 7-second pirouette.
Oncard creasing:
Everytime you bent the cards, you break some paper fibers. The more you bent them, the more fibers you break. Eventually, the cards will develop weaker spots where a crease will show if the card is bent sufficiently. All cards get to that point in time. And the way you use your cards will determine where the crease will appear (have you noticed that the creases are all located approximately at the same locations on every card?).
Some moves are harsher on the cards than others. Springs, Lepaul spreads, riffle shuffle and bridge are particularly stressful on the cards. When doing these moves, make sure you do them on both sides of the decks, in order to even the stress on each side of the cards, and break the fibers as evenly as possible. This will help use you deck longer. Using a porper clip will also help your cards get back flat while the stress is release from the cards, this might save you some extra springs the next you use your cards if you like your cards flat.
On card lifespan:
When beginning I used to change deck every week or so. The more I got comfortable with a specific move, the longer my cards would last. That's because I developed the right amount of hand strength and control to apply just the right amount of pressure, and to avoid overbending the cards, which I did a lot at first, only I did not knew at first how wrong I was doing it.
Cards are made of paper, they don't last forever. I suggest you use cheap bikes to practice a move until you are comfortable doing it. Then you might want to use you more prized ones.
Also, don't throw you used decks away just yet. You might find later on that those are in just the perfect state for some other moves...