Assistance with Simple Euler Physics Integration

So, I’ve been picking my brain for a couple days on this problem, and I haven’t come up with a solution as of yet. I need your help!

I’m using LibGDX and am trying to create VERY simple physics for smooth, 8-direction player movement, using acceleration, velocity, and position vectors. I set up my physics equations (according to the Euler method) in my “isRunning” boolean, and my input works fine, but the physics are wonky and send my “player” accelerating infinitely in the positive y direction. I would post a gif of the program running, but I’m unsure as to whether or not that is actually allowed on the forum.

Could you guys assist? Thanks in advance!

http://pastebin.java-gaming.org/ce500034f0317

Also, on an unrelated note, this is my first post on the forum! =D