Rear derailleur is messed up I have no clue what happened to my derailleur on my bike. I can ride the bike and after a couple of cranks the chain gets really lose and seems like it's about to come off so I stop pedaling and wait and then the tire does a couple of rotations and the chains tight again.
Chain looks too long to me.  Shorten the chain.   

Not gong to guarantee that will fix the problem but it looks like part of the problem to me.  

Park Chain Sizing

Park chain cutting