You sound a lot like me (See my post about my wife falling out of love with me to see how that's turning out...). I tend to give myself completely over to the other person, to the point that my happiness and emotions depend on them. I basically lost my own sense of self in the process and now I'm trying to rediscover myself, and hopefully save my marriage in the process.

As for worrying all the time about the relationship and how it could go sour, did you have a previous relationship that ended badly? That was my problem, and now in relationships I cling to the other person hard it repels them, and I worry that if I don't keep them happy with me 100% of the time they'll simply up and leave.

That's not a strong individual, and that's not what someone wants in a partner. Take time for yourself, as you say above. Become strong and confident and able to stand on your own 2 feet, and then if you choose to be together it's because you choose to, not because you need them to lean on and support any insecurities you may have.