How to stop advances from my coworker??

Hey everyone, so i just started working at target 4 days ago and i’m already receiving advances from a guy i work with. I thought he just wanted to be friends at first but low and behold that was not what he wants. i’ve expressed multiple times that i have a boyfriend who i live with and yet he still persists. i gave him my number when i thought he just wanted to be friends and he won’t stop texting me. it’s not really harassment because it’s just very innocent conversations but he compliments me and last night he asked to talk on the phone. i said that i didn’t think my boyfriend would be comfortable with that and he apologized but i checked my phone this morning and he had texted me saying i’m the most beautiful girl in the world. am i doing something wrong?? i’ve never flirted back with him and i rarely reply to the messages unless it’s work related. i just don’t know where to go from here. i don’t want to go to HR and start drama especially since i’m new but i can’t think of anything else to do or say. he just can’t take a hint! please help or share similar stories. i don’t know what i did wrong.