You want true love and a relationship that will last, but you keep getting in your own way of letting that happen. One minute you're involved with someone special and dreaming of the long term, and the next you're feeling restless and pressured, as if the relationship is cramping your personal style, hindering your ability to be yourself and go where you want to go in life. Who knows?
Maybe it really is, but if so, it's likely because you're subconsciously attracted to relationships that will present a challenge to your personality and your goals at a basic level. Since shorter or less committed relationships work out fine for you, you may decide that's all you can handle, and go through a string of those before you finally start to realize that your love life isn't as fulfilling as you want it to be. Don't delude yourself into thinking you're just not 'the marrying kind'; if you want love and intimacy and partnership, you are. Your challenge in life is to figure out how to make a long-term relationship work. How can you get past the feeling that your independence is challenged by intimacy with a lover? Remember, for one thing, that practice makes perfect.