Routing help with two NICs CentOS 7 [bare metal]

So I recently installed a second NIC in my Dell Optiplex 7010.

I had this idea that I could have one NIC bridged for a couple of VMs utilizing a specific subnet/VLAN, while the other NIC was for the host traffic on the default subnet/VLAN.

Before I jumped into the VLAN configuration, I wanted to test with the following scenario:

Currently, I have one NIC (p2p1) connected to a router that serves DHCP addresses from 192.168.1.0/24 and the other NIC (em1) pulls from a different router serving addresses from 192.168.128.0/24

I would expect to be able to specify my interface during a ping test, ie:

ping -I p2p1 www.google.com 

and

ping -I em1 www.google.com 

however only one is able to reach the internet at a time.

My suspicion is this is related to the routing, only registering one gateway address for internet bound traffic at a time (192.168.128.1 or 192.168.1.1)

Can anyone offer some insight into this situation? I feel like I may be missing something fundamental.

Cheers,

edit: Oh and for what it's worth, this is a headless server, I have NetworkManager disabled, and am configuring things via /etc/sysconfig/network-scripts/ifcfg-em1 and /etc/sysconfig/network-scripts/ifcfg-p2p1

I will be happy to share these if necessary. But again, I'm concerned my concept may be flawed.