Fear of committment or never met the right person

[start-fresh]

I'm in my mid twenties and have never had any relationships last beyond the 6 month mark, and can't help but question myself on this topic. How do you really know which of the two is happening? I always tell myself when the relationship ends that we just weren't right for each other, but then I usually end up regretting the break up at some point. I think I might try to find fault where many others wouldn't, thus leading me to only have short term relationships. At the same time though, you always hear that when you meet someone truly meant for you there won't ever be doubts. Does anyone have any thoughts?