When he says "i love you" before you love him yet? ?

so ive moved back home after college and ran into my highschool sweetheart, who was looking for a roomate. I thought this sounded good, we HAD been best friends for years before i left state. And after living together for 6 months, we had thought we should start dating again, and its really going great.

The problem is, he's told me that he loved me. what do i do?? i used to love him in highschool and i would like to love him again someday. But i dont feel that way yet, which ive explained and he understands.

but he keeps saying it! like after sex or when i leave. When ive asked him why he keeps saying it, while knowing that i dont feel that way yet, he just says he cant stop himself. What are some nice ways to respond to this? I dont want to pretend to love him, but i feel bad just smiling and nodding. Help?