As the future heir of the Quan Family, Quan Sicheng absolutely couldn't have an affection for men.
Let's not mention what his sexual orientation might be in private; at the very least, publically he couldn't have any improper contact with other men.
This was not just a matter of the family's reputation.
There was another, more important reason.
The next generation heir.
Quan Jinbei had adopted a child early on mainly because he was born weak and had been told by fortune-tellers that he wouldn't live past thirty.
In such circumstances, the Quan Family had to determine a new heir early on so as to stabilize the Quan estate.
Conversely, if the Quan Family heir was exposed for liking men, potentially leading to no one to carry on the lineage, then the industry that the Quan Family had built over many years might very well falter without a successor.