When this happens to me I'm usually looking for a problem with the relationship so I have a reason to break up.

I've done this because I'm afraid of the unknown and I'd rather do the whole thing (find a new person, 1st starbucks, 1st trip, etc etc all over again and again).

I've done this before because the honeymoon phase wears off and I run out of ideas - I've dated a lot of people to create experiences for myself, without specific regard for the other person.

Maybe you're in a frame of mind where you might think that you can't have a meaningful relationship right now - and that any relationship you're getting into now isn't going to be "the one" so it has trivial meaning and point to sustain.

Sometimes I feel like I can do better and that I'm settling and that pretty soon something bad is going to happen that will solidify that relationship into something that I won't be able to escape...

It sounds to me though that you want to be chasing girls and you need to just do that for awhile and figure out more about yourself