So, me and my best friend started chatting with this boy from our school over instagram and we kind of got to know him a bit. Once we all became friends and started talking daily I began to develop feeling about this boy. Feeling that I have never devolped about any boy. I think it was the feeling of love. My friend had a relationship with him then he dumped her. I had a relationship but then I dumped him! It was a stupid mistake! But now my friend and him have a really strong relationship and they even went on a first date together. Now my feeling for him are getting stronger. I am kind of jealous but I have to hold my feeling in. It sucks!
What do I do?

You back off if he is already taken.

You make your focus passing your middle school classes and as Tickle said - back off.

Yes it sucks to have feelings I suppose, but you have control over those feelings right? Then you deal with them in a mature way by respecting their relationship, and YOURSELF, and not obsess over your own feelings of jealousy, or attraction.

You may like him, and this may be your first time having those feelings, but it won't be the last time, nor the only time you find that some things in life do suck. You just will have to learn to deal with these situations, and get through them without giving up your dignity, or self respect.

The feelings will pass eventually if you get on about your own life, and the other things besides him, that are more important to you.

Be happy for your friend, and leave it alone. Find someone else, or just do nothing.

Men come and go... crushes come and go... best friends are forever.

You have to hold your feelings in with him, but not with her. Best friends tell all. Laugh about how lucky she is and what a fool you were.
You weren't a fool, but don't say so. He sounds a bit fickle to me.