He didn’t though. He resisted and rejected it continually.
Not quite; throughout the three seasons of TOS, he did open up emotionally in defining ways relevant to his bonds with humans, though not limited to:
"Where No Man Has gone Before": Spock--despite spending most of this second pilot coldly pushing Kirk to murder Gary Mitchell, the episode ended with a revealing admission:
"I felt for him, too."
Even during this early stage, Spock was not completely suppressing emotions, as much as he tried, and part of his disease-induced honesty as seen in
"The Naked Time" proved strong feelings were there (his love for his mother, friendship with Kirk), and it was emotionally draining on him to suppress those feelings.
"Amok Time": Spock is quite open in recognizing Kirk and McCoy as his friends, and--the following is key--
after the effects of Ponn Farr had passed, his reaction to seeing Kirk alive was--as McCoy so accurately described it--
"...an emotional scene that would have brought the house down!"
Late in season 2, we have
"Bread and Circuses", where Spock and McCoy--after surviving the first round of gladiator fights--have this exchange:
McCoy:
"Do you know why you're not afraid to die, Spock? You're more afraid of living. Each day you stay alive is just one more day you might slip and let your human half peek out. That's it, isn't it? Insecurity. Why, you wouldn't know what to do with a genuine, warm, decent feeling."
Spock:
"Really, Doctor?"
McCoy:
"I know. I'm worried about Jim, too."
Spock is unambiguous here--about having--as McCoy described it--a "genuine, warm, decent feeling"--with his "Really", which was--as McCoy correctly concluded--Spock worrying about Kirk.
During season three's
"For the World is Hollow, and I Have Touched the Sky", we see Spock gently supportive of McCoy (recovering from the Oracle's punishment):
McCoy:
"Oh, that Oracle really got to me. I must be especially susceptible to its magic spells."
(McCoy notices Spock's help and behavior toward him)
Kirk:
"Spock knows."
Spock's feelings for McCoy were so strong, he did not need to utter a word with the expression on his face, and his helpful nature. The overall point being that TOS Spock maintained a certain amount of his Vulcan stoicism, but he--if actively--tried to reject his emotions, the key examples of his open emotional behavior would have never come forward time and again, no matter the circumstance.
But there… what else do you need? The reason they couldn’t pull another Spock/McCoy relationship out of Data/Pulaski is that Spock and Data are totally different characters. So far from being ‘clones’ that it’s not even funny.
Well, you're acknowledging that Pulaski was used to be the McCoy clone to the one character placed in the Spock role: Data, which was my point about Data's role on TNG.