Is it normal to be this clingy/jelly by friends?

You don't want to stop because it is rewarding for you: even though it is the same thing that is going to destroy those relationships.

Get to the root of WHY you need so much extra attention and love from people. You might even want to ask a professional counselor to help you find this answer because it's difficult for some people to be completely honest with themselves about what is really going on in their lives. A professional will ask you the questions that you should be asking yourself: they won't provide you with a tidy piece of advice that will miraculously cure you. This kind of stuff takes years of growth and persistence on your part to correct, but the freedom you will gain in the end will be so worth the time and frustration.

I think your first step would be to treat the attention you seek like a bad habit; like smoking, drinking, cursing, etc. Spend a week just observing yourself and write down the moments when you crave attention and also when you receive attention. Once you've done that, review it. See if there are times when you think you could have done something on your own, but you didn't. Imagine (visualize) that same scenario, only instead of having other people around, imagine doing it on your own. Picture yourself being comfortable and confident doing it on your own.

The next time a similar situation comes up, practice denying yourself first. It probably won't feel good and maybe a little scary, but that's just because it's unfamiliar. Afterwards, you will feel so proud of yourself for taking a step in the right direction. Once won't be enough to cure you. Even a dozen times won't, but every time is practice that will eventually lead to a new positive habit.

Another thing to work on, is viewing yourself as adequate company. If you like yourself, then being with just yourself is not as lonely.