Your bow arm should be straight. Your bow arm should not be locked (like double jointed people lock their elbow). If your arm is straight it will not fatigue nearly as quickly as it would if you bend your arm which will allow you to shoot more accurately and over a longer period of time.
A bent arm is just as bad as a locked arm.
Your problem is likely one of two or three things or a combination of all of them.
#1. Your draw length is tool long causing you to stretch farther than you should.
#2. Your release is way too long causing your anchor point to be too far back thus causing you to be stretched out too much.
Both #1 and 2 will cause you to lean backwards with your body and you will get arm slap and left and right inconsistencies.
#3. You are gripping your bow instead of just allowing the bow to rest on the pad of your thumb. Hold your hand up in front of you and bend your wrist as if you were telling someone to stop. Now rotate your hand to make a "V" with your thumb and index finger, Rest the bow in the pad of your thumb and allow your fingers to RELAX in front of the grip with out actually gripping the bow.
No offense but that first video above is a joke. I wouldn't have that guy coaching any one on proper bow form. The second video really doesn't show much of anything.
Watch this video below about the "TRUE SHOT". It shows you a real proper grip. You can do the same exercises with out the true shot if you consciously make an effort to concentrate on proper grip and not hitting the bulls eye for a week or so.
http://www.youtube.com/watch?v=hAyMc6uvavg
Here is a good video showing proper form from several angles. Notice his bow arm is straight but not locked and his body is perfectly straight up and down and his arms are forming a perfect "T". Never mind him taking off his shirt but it demonstrates well how you should be shooting your bow.
http://www.youtube.com/user/arqueiro1400?blend=22&ob=5
Here's another good video for you to watch.
http://www.youtube.com/watch?v=Nm5bA...eature=related