My (23F) boyfriend (24M) is obsessed with random depop girl and I'm not sure what to do

my boyfriend and I have been dating for 4 years. We've had ups and downs but I love him and he loves me. We live together, see each other everyday and spend quality time together. Or so I thought.. recently I have been feeling really insecure about our relationship and I just realized why after catching him in a weird lie. basically he has been obsessed with this random girl who he follows on TikTok that also has a depop account. He buys her clothes, he's been wearing her hair clips, and she's in his phone background. he lied about how long he has known her and he didn't tell me until I caught the background in his phone. I have no clue what to do bc he seems to be into her and obviously I don't want to leave him over it but as a gf idk what else I'm supposed to do when it seems like he is over me and into her. I tried to talk about it and bring it up but he doesn't think it's a big deal at all he says it's just a dumb celebrity crush for him and that he loves me but I'm hurt he didn't tell me. He says she doesn't even follow him and that he thinks she doesn't know he's the one buying everything but it seems weird to me. what's my next step here bc I'm 100 confused