He is her childhood friend.
Ruminas had an infatuation with Chloe due to her intervention with Veldora. Ruminas viewed Chloe as her savior.
Until the intervention of Rimuru, Hinata and Chloe were the same beings. Once their souls were relegated, they became two separate beings.
Due to her ability to leap backward in time, she was both Shizue's student and mentor. The two had a healthy respect for one another that set the tone for each becoming a hero.
Chloe was one of his students. Even though in the beginning she was wary of him, little by little she started to respect him as her Sensei and regards him highly to the point that she said that Rimuru is the key to change the future. And among the children, Chloe was the one with the most affection towards Rimuru. Eventually, that affection grew into attraction, as Chloe considers herself as one of the contenders to be his wife along with Milim, Shuna and Shion.
This affection is most obvious when the spirit of her future self gave Rimuru a kiss right before inhabiting her child self.