Little sis,
I lost my virginity when I wa 12, and been with the most guys I'd ever been with by age 15. I wasn't brought up in a christian home, and I didn't really have a lot of wisdom like I do now. It sounds to me like you have a better head on your shoulders than I did.
You'll find it really is up to you now to set boundaries for yourself. No one else will do it, and it requires self-control, something that doesn't come by just doing what feels good. This is hard, I'm 25 and still struggling with self-control. You are at an advantage because you already have put a stop to it going to far and realize it's not something you want to partake in.
The key here is protecting yourself from temptation. Don't say to yourself "Oh, I know I won't do it, but it's ok to do heavy petting....I'll be able to say no". Some christians, adults included, have found it's necessary to set the boundary to no kissing. I'm not saying this is a set rule, but only you can decide for yourself the necessary boundaries that only you can make. No one else can set those boundaries for you.
You are so young and realistically probably won't be getting married for atleast a few years. You know that's where God's boundaries lie. If you partake in make out sessions now, which are indeed very stimulating, remember, I've been there.... how are you going to hold out for so long?
My recomendation is consecrate yourself to God now, seek to fully obey him and honor him, now you know that you have already exceeded a boundary and have entered dangerous teritory. If you do indeed go all the way, you'll find it'll be harder to say no, and like what happens to most females once they go all the way, they end up having several partners. It's up to you to decide if that's the route you want to go.
Plus, boys, especially teenage boys do not have the capacity to commit and love you like you truly need. They will not respect you and they will tell you they do, and that they love you..... however, you are venturing into an activity that will result in a loss of respect for yourself, and from others, including the boys who partake in it with you.
Honor yourself, and honor God with your body. You are special, treat what you have to give that way.... and don't give into those intense feelings.
The best ingrediant for a happy, lasting long term marriage relationship is first of all being chaste unto God, and having a relationship that is built and mutual love for God..... not on one of lust, which is what those strong feelings you're having is.
Take it from someone who's had a lot of experiance in this area and learn from my wisdom and mistakes. Good luck and God Bless.
HB
