Need immediate help

I try to be mature hence my age but with my jealousy its a little hard to maintain that maturity.

Well, it is mature that you realize that jealousy places its limitations on you and therefore do not attempt open r/s which are not for everyone. Shows good judgment. Also, jealousy may loosen its grip on you as you get older. You won't necessarily need to suffer like that all your life. At any rate, it is a normal human emotion and nothing to be ashamed for.

Jealousy can also be a function of love. Stronger feelings for her - more jealousy. Does not always hold true, but frequently enough.

Yeah I can see that I jst hope i dont make the same mistakes I did in my last relationship cause truthfully this is my first relationship in a year

TBH, Jealousy stems from insecurity and fear. It is common but not an empowering feeling at all. More than anything it will hinder one from truly loving the other person because with jealousy usually possessiveness and controlling behaviors can develop. yes it is true that if you are jealous because of a friend or loved won, it's likely that you're very attached to them but it's definitely a feeling that you want to keep at bay as much as possible.

I understand that you want her to love you and just you but you said you would be there to support her decision no matter what. You guys were friends before crushes and I know it will be tough. Try taking your mind off of her and do activities. When she sees you maybe she will change her mind.