my (20f) bf (18m) doesn’t see an issue with the girl who is obsessed with him

please tell me whether i’m being a delusional / crazy jealous gf, or if i am within reason.

last night me and my bf went to a party with loads of his family and friends. there was a girl there (17f) who has had a crush on him in the past. she has a boyfriend now, and obviously my boyfriend is with me, but they used to like each other, and their families have been friends since they were kids.

my bf and her had a conversation a few months ago (we were dating at this point), reminiscing about a night they spent together at a group sleepover, when my boyfriend said to her “i would’ve kissed you that night, but i was too scared”.

he apologised after i had a problem with him saying that to her, realising it was wrong. so that’s all water under the bridge.

also before we were together, she used to send him nudes which he would wank over.. so it’s clear that he had a strong physical attraction to her.

last night at the party my bf was annoyed at me. i was tired and not drinking, but everyone else was drunk and having fun. i was not in a bad mood at all, i was just exhausted as it was nearing 1am and i’d been up since 7am. so he was annoyed and avoiding me.

i ended up walking back to my bfs house by myself – 20 mins, in the dark, alone, 0°c, and everyone else got home about 30 minutes after me.

when he got home, he told me i ruined the night by being in a bad mood the whole time. i dampened the mood whenever i came in the room, so he had to keep running away from me. i said i’m sorry, he called me a liar.

he really hurt my feelings. then, the girl texted him asking if he got home okay. i thought it was weird since she didn’t text anyone else to see if they got home okay, plus they all walked home in a group. and i, who walked home alone, did not receive a text from her seeing if i was okay. JUST my bf. then they were texting a bit before bed.

this morning she had posted a selfie with him and some other people on her story. i told him i was upset that he didn’t take selfies with me, but he took some with her (+ others). he also never kissed or hugged me all night, but he was kissing (on the forehead) and hugging other people, including the girl’s mum. this girl’s mum, btw, used to tell my bf she wanted him as a son in law. she also told my bf last night “we love [girl’s bf], but you know how much we’ve always loved you…” he entertained this by responding “your whole family loves me!”

so i’m feeling really hurt and jealous this morning. i told him all of this but he got defensive and said i’m overthinking it too much and there’s nothing to feel jealous / annoyed about.

please tell me if i’m being insane about this!

TL;DR – my bf avoided me all night but spent time taking photos with and texting the girl he used to have feelings for