Can you confirm that this thread is about your CentOS 7 system from this thread?
One method to move /boot from /dev/sdb1 to / (/dev/sdb2):
mount /dev/sdb1 to something else like /mnt/oldboot
cp -rp /mnt/oldboot/* /boot (make sure files are copied successfully)
Comment out or delete the /boot line in your /etc/fstab file.
Boot from the CentOS 7 DVD and select rescue mode.
Once at a shell prompt follow the instructions for chroot
Since you have two drives do you know which is the boot drive? Usually it would be sda but your /home is on sda and the OS on sdb. I can't tell if your using a legacy MBR or UEFI. Legacy BIOS and MBR would be:
As a note for others who might be interested since the OP is actually using LVM do not move /boot from its own partition.