How do you keep a 17 year old guy when he leaves for some other girl. When he says he wonts to marry me. When we broke up he wonts to be best friends so if something happen he can come back I would take him back I think. But is that the right thing to do.

I think he might be playing you along. If you liked someone would you go out with someone else and keep them as a friend 'just in case' it didn't work out?
If this isn't consistent with how you think you would act, then you probably don't have much of a basis for a relationship here. At least not at this stage.

One thing I have always found a TOTAL turn-off is a person who is needy and desperate to be with me. Once I get a sense that their live is structured around me, and wanting to be with me all the time, I run away.Move on, don't keep hanging around waiting for him to notice you, find new interests, hang out with friends.

Sounds like your "cake".

"He wants his cake and eat it too". That means he wants other girls and if/when it doesn't work out he still can go back to you.

You are worth more than how much this boy likes you. :(

Value YOUR WANTS AND NEEDS above his. CHOOSE YOU. <3

He's hurting you and that's not okay.

Never make a boys wants or needs more important than your own.

Boys are fish... there's always another one that's going to swim in your direction for you to catch.

"He's a dime a dozen", meaning there are more out there... for you.

It's time to kick this one to the curb... he doesn't respect you. He's NOT WORTH IT.

I want you to feel happy and good about yourself. As you should. You have to explore other options and believe that you deserve respect just because YOU DO.

(Look at your life a little closer perhaps. Are there people in your life that put up with boys/men that treat them with a lesser respect?). Just askin'...

Be your own best friend and protector. Be good to yourself. Require MORE from your boyfriends... after all you areeee worth it! Xo :(