Upset about the past-Longish

Basically I can't stop thinking about the past and how upset I am that it happened. Up until the age of 14 I was bubbly and vivacious and popular with tonns of friends. I was a happy, confident girl. Then I met this girl who became my best friend and suddenly she was the leader and everyone wanted a piece of her. This bothered me a little but not greatly and then our friendship group broke into little factions and I was left alone.

So I was a loner with no friends and no one knew me when I was 15-16 and I spent every weekend and those two summers alone at home. By the time I found some friends in year 12, I was experiencing many things for the first time like going out, getting drunk, actually meeting new people. So that by the time I turned 17 I still felt so immature and like my teenagehood had been stopped for two years. When I turned 17 I still felt 14 but in the end my friends ended up giving me so much experience. By the end of my 17th year I felt my age, finally. But I always look back on those years and feel cheated because even now I have pretty much dated ideas on life e.g. I still think the idea of boys and sex is scandalous and that Im much too young to date someone who's 20 when I myself am 18. I always think that if I hadn't lost those two years I could have crammed a bit more into my teenage years and would be further along with my growth (social, psychological, emotional). I realise that Im a late bloomer when it comes to boys and everything else but its only because I was left behind before. Also that time of my life messed me up in others way and I was exceptionally sensitive and demanding with my friends-people would actually hate being around me because I acted so sensitively.

Also when I was 17, I had to go into counselling, I suspect, due to that time in my life where I was depressed and suicidal. My attitude to relationships was all wrong and even now, I'm trying to remember to be much less clingy to my new best friend. There's really no question here but I wanna know how I can stop looking at the past with regret? And how can I move forward?
Thanks for reading.