(17F) and bf (19M) .. I am insecure of him being with another girl

I
Okay well our start was weird he was legitong laying options who to chose me or some another girl and he liked one girl that time ..
He proposed me i didn’t know I was an option after like 6 months of us and the day he proposed me after some time the girl proposed him too that he liked he said no ..
Well after 6 months i he said if she has proposed a little early he would have gone to her .. ( so he was leading me on) and the. Said but now I only love u
Then we had a brekaup for sometime after some months I get to know right after our breakup he proposed to the same girl . When she rejected he liked someone else
And gave her book with personal diary
Now she became his friend and she sends him bookstore date and dancing together reels .. and now he is back to me
.okay now today he said I will watch movie with another girl and I want to dance with that girl who send him reels
What should I do?
Am I being insecure?.
He never physically cheated and said that he would never kiss and i asked him if his dad did the same watching movie with someone else how would ur mom feels he said they are married we are not
Or should I let him have fun ?

Tl;dr he is going with another girls and he even had watched his city with many girls .. am I right being insecure? And ik two girls he used to like .. and he is thinking of going to dance with the girl he liked and movie with his friend