The following contains spoilers for Thor: Love and Thunder, now playing in theaters.
During Thor: Love and Thunder, Quill had to give Thor a pep talk to remind him that the only way he can continue to find out who he is as an individual is he has to learn to live with his loss and look to those who still love him. Before the team left The God of Thunder, Quill inspired Thor to continue searching inwardly, and it may not have been something that Quill wholly agreed with, as he may be lying to his team about his search for Gamora.
In the conclusion of The Infinity Saga, Thanos took Gamora and sacrificed her to obtain the Soul Stone. While the Sacred Timeline's version of Gamora was lost forever, another from just before Quill and Gamora met found herself in the modern-day. Rather than stick with a family she never knew, she went off on her own to explore a galaxy she hardly recognized. However, Avengers: Endgame showed Quill searching for his lost love and quickly hiding it when his crew returned to the ship.
Unlike the rest of the Guardians, Quill's Terran nature meant he was often the more empathetic of the crew. While they already mourned their friend and knew this version wasn't the same, Peter never could accept it. Therefore, it's possible they tried to convince him to stop searching and let fate decide, but even though he may have agreed, he didn't keep his promise. Now, he's continued searching for and trying to connect with his lost love behind the back of his family.
While affectionate to one another, the team has always been practical regarding matters of the heart and how they affected their present situation. As a result, it's possible their potential reaction to Quill's efforts may have kept him from ever wanting to tell them. In doing so, his fate may have been sealed, as the team would've still heard him out, especially since Nebula would've likely wanted to see her sister again.
For now, the future is still unknown over how the team may react to this secret that Star-Lord may be keeping. On the one hand, they may understand his hesitation and desire to keep searching. On the other hand, there's an equal opportunity they would be hurt if they weren't trusted enough to confide in. Should the latter be the case, this would drive a wedge between their dynamic and test them in a way they've yet to experience.
To see Star-Lord allude to his secret Thor: Love and Thunder is now playing in theaters.