Why do we push??

Why do we fall for someone so fast, yet we push them away? I know that emotionaly trust is a huge issue. But I am determined not to let it ruin my next relationship (if that chance ever comes again). Does everyone get overly jealous and extremely needy? I trust the one up above that he has a plan for me and I've heard that he does not give you more than you can handle, but why did he choose me? Somedays I can not take even the slightest rejection. I read into things way too much which sends my emotions into a downward spiral which can only be stopped with the contact of others. I reach out to empty air, grasping for anything. My hope is to find someone, that lets me grab ahold but does not take advantage of my scars.