There could be many reasons why your relationships do not last long.

That's my theory

Maybe you're looking for the wrong type of man, the kind of man that is not interested in a serious relationship but only for a "good time." Maybe these men are immature and can't make a commitment.

On the other hand, you should probably examine your own  actions. Maybe your boyfriends are scared off because you are taking things too quickly. Maybe you are placing unrealistic expectations on them or on the relationship that are causing you to be continually disappointed.

Just because you're pretty and have a car and a good job doesn't guarantee that you will find a husband,

Yeah, it's only women that look for those things in a guy.

because a meaningful relationship is built on so much more than that. If you want to attract and eventually marry a man that will be devoted to you, appreciate the person that you are (and not just looks which are temporary anyway), then you need to cultivate the inner qualities that he will be seeking. In other words, to find the right person, you need to be the right person. So try not to worry so much about looking for someone. Focus on your own growth and goals in life, and then wait for the right one to come along to you in response to the inner beauty that he sees.

Remember also that true love is difficult to find but it is worth the wait. Try to be patient!