I need your opinion /lovelife

I wasn't gonna post this, but lately i've been so sad and so distraught, so i need someone's opinion.

(Sorry for my english, i'll try my best to make this understandable(??)

Okay, so i'm two weeks into a relationship with a guy, we're gonna call him alex, and i've never been so SO SOOO in love. I know i said i'm just two weeks into the relationship, but i've liked him for quite some time and i've always liked him (physically). I'm and insecure person, like VEEERY insecure, but i try to not be so annoying about it, so i just keep things to myself.

THE THING IS, when we were just friends, we would always talk about the people we liked, and he always talked about this girl (his ex) in such a beautiful way but she was a bitch (i'm sorry), she was a dick with him and he always found a way to make it "not her fault", until he eventually started to get over her and "fell in love" with me (idk). Since he told me he likes me, i've always felt insecure about her, because she's beautiful and two years younger than me (btw, alex and i are both 2007).

I started to remember how he always talked about her with so much love and hope of getting back to her, and i've been thinking that is weird how he suddenly stopped mentioning her and now he likes me, OUT OF NOWHERE?? I've already talked about this with him, i told him about how i'm insecure and i wanted to know how he feels about her, and he told me he doesn't feel anything (OF COURSE, YOU'RE NOT GONNA THROW SHIT TO YOURSELF, ARE YOU?).

This is hard because even tho he hasn't given me any reasons to be insecure or jealous (besides his storytimes while we were friends), the only thought of that girl makes me nauseous, dizzy and my eyes get crystralized, it's so frustrating that THAT topic has such an impact on me. I think he thinks the topic is closed, like it doesn't affect me anymore, but seeing that he still follows her on ig (they're mutuals) and they're still friends on facebook, even after i told him how insecure she makes me, makes me wanna cry. I don't wanna be like "WHY DO YOU STILL FOLLOW HER AAAAGHHH??", because i think it's common sense to simply ELIMINATE from every social media the girl who makes your gf insecure, but idk man.

I didn't want to mention that topic again, but yesterday i was at his parents house, and his cousin was there too. We were eating and they start joking about they're exes, like, his cousin was making fun of him and he was making fun of his cousin. Now this is what broke me completely, because she (his cousin) started talking about this girl and how alex was so crazy over her, how he chased her even after she treated him badly, the thing that is stuck in my head is how she said "that relationship lasted over a year, right?".

 I swear to god i wanted to throw up so bad, i felt physically ill, like everything was blurry, i didn't wanna talk anymore, i had to bite my tongue to prevent myself from crying. I just sat there in silence and the atmosphere turned so awkward, they both stopped talking and threw little glances at me, while i was trying so hard to not break infront of them. I made eye contact with my boyfriend (alex) and i almost lost it, because he seemed so lost, like he didn't know why i suddenly shut the fuck up, i had to look the other way because my eyes were so watery.

 Then he took me by the hand and said "let's go wash your hands", while i was washing my hands he asked "what happened? Why did you get so quiet out of nowhere?", i said i was fine and nothing happened because mentioning how his ex makes me so insecure and how his cousin mentioning how much he loved her makes me want to rip my face off and dissapear is too much and too awkward.

There are many other reasons of WHY his ex makes me so so so insecure, but this is like the "short version" of the story. What do you guys think i should do? I'm still thinking about the things his cousin said and i can't help but feel physically ill. I love him so much and he's such a good, caring and loving boyfriend, but my insecurities are taking over me :((. I don't know what to do anymore