No, Valentine did not believe Jace was his son. Valentine was obsessed with creating a perfect world free of mundanes and believed that only those with angelic blood were worthy. He saw Jace as a tool, a weapon to be used in his quest for power.
Valentine viewed Jace's angelic heritage as a means to an end, a way to manipulate and control the Shadowhunter world. He never truly acknowledged Jace as his son, nor did he treat him with any affection or paternal care.
Valentine's actions throughout the series, particularly his attempts to erase Jace's memories and his willingness to sacrifice him for his own goals, demonstrate that he never saw Jace as a son but rather as a pawn in his twisted game.
