If the Jedi of the OT forbade romance/marriage/etc., then wouldn’t this little taboo have been hinted at somewhere in the OT?
Why would it need to be hinted at in the Original Trilogy? Luke was on a need-to-know basis throughout the entire Original Trilogy. George Lucas only revealed the most vital elements of the backstory which were absolutely necessary for the audience to understand the plot and the characters.
However, I would still say that it is indirectly hinted at in the Original Trilogy. The Jedi Order was spoken of as an ancient religion. The only Jedi whom Luke encountered were Obi-Wan and Yoda, who were both single and celibate and who both wore monk robes. George Lucas gave every indication that the Jedi Order was a monastic order of warrior monks.