Given the comments that are made regarding Mike Collins' 'loneliness' while flying Columbia around the far side of the Moon on Apollo 11, would I be right in assuming that the Apollo 10 CSM and LM were always on the same side of the Moon during their flight, since the LM did not land?
Your assumption is correct.
The Apollo 10 LM, Snoopy, initially went into a lower, faster orbit than the CSM Charlie Brown, but then shifted into an eccentric orbit with a higher apolune than the CSM in order to let the CSM catch up. The two spacecraft were in direct radio contact throughout the flight, as you can read in the flight journal transcripts, including periods when they were behind the moon and out of Earth contact.
Apollo 10 Flight Journal, 099:56:00 to 101:45:00
Apollo 10 Flight Journal, 101:45:06 to 103:44:50
Apollo 10 Flight Journal, 103:44:50 to 105:32:45
I reckon the 'loneliness' referred to by Collins was due more to his being alone on the CM while Armstrong and Aldrin were on the moon. For the 'dark' phase of this orbit he was also out of radio contact with Houston. Apollos 8 and 10 by comparison has more than one astronaut on board the CM during lunar orbit. Of course, Collins had plenty to busy himself with as the trickiest manoeuvre remained to be done: rendezvous and docking with the LM. The latter was by no means a foregone conclusion and if it failed then Collins would have to return to Earth alone.
But NASA had picked the right man for the CM job and Collins saw off his 'loneliness' - and many bigger distractions like the stink of the CM's "men's room" - for the remainder of the mission.