Hmm. Not sure what you are saying there.
.
When you use VM, you have 3 choices for your virtual network,
NAT; it will share the same NIC as the HOST PC,
Bridged ; the NIC will be use only by the VM
Internal: not usefull here
NIC 1 ( bridge ) ; use by PFsence in the VM to connect to the WAN, example a cable modem
NIC 2 ( bridge) ; use by PFsence to connect to your switch
NIC 3 ; use to connect the host to the switch
with this setup it's like if you are using PfSense in a dedicated PC , depending o the VM hypervisor it can be very hard to make your PCs on the network communicate with Pfsense if you are using NAT
here a small drawing, the VM is represented as a smaller pc inside the host