Dear Paul,
You wrote that there is something in your girlfriend's character that you can't accept, which causes friction. If it's embedded in her character it isn't likely to change. Don't drift deeper, and marry by default. Think it through rationally amd make a decision. Then act.
You may need to carry paper and pencil with you to write things down over the period of a week or so. It may be the only way in your "obsessed" state, that you can catch facts you need as they come to mind, so that you can examine things clearly.
Here are some questions to consider: how serious and deep is the flaw? How old are you? How old is she? How soon will you have jobs and graduate, if you are still in school? How bad are the difficulties caused? Can you bypass the situation to overcome it? How difficult would it be to live with this flaw through a lifetime together? Is any of the problem your fault?
Regarding how deep the flaw is; consider these two examples and see how they relate to your concern. There is a big difference between lying, and keeping a messy house. (A messy house is different from being a dirty housekeeper, which can cause illness.) Lying is very serious, especially if it is habitual, or about something that is important to trust. Sometimes a person lies for self-protection, or fear, so conditions that bring on lies. That possibility would need to be taken into account. A messy house may be overcome or bypassed. For instance, by helping her and doing your part;getting household help;or by deciding together to always live very simply. If you can't learn to ignore it, help, or work around it, you had better stop before you get in any deeper. Her life will not be happy if yours isn't. This is important to the welfare of you both.
Is it possible to discuss this truthfully and rationally with her, if you choose your time well and tell her how important it is to both of you? The answer to this will tell whether she is a person you can consult and cooperate with about many other important things that would surely come up in life together. If you manage to arrive at a mutually satisfactory and workable conclusion to overcome this problem it's a good sign.
In the messy house example: would you be willing to help clean and tidy, or would you make a mess, leave your stuff around, and expect her to clean it up? If you're part of the problem think whether you can change yourself and stay changed. Would she change and stay changed? These are more important questions.
You said you only have experience with this one girl so you feel you don't have anything to compare. You can observe others fairly closely, which gives you have perspective; especially family members whose true lives are more open from hearing stories and seeing actions and results over a period of years. The long time frame is valuable. This considering is all part of your education. Consider the lives of your friends, their parents, your parent's friends. You can reach conclusions about families with relationships closest to the kind you want or don't want. For instance, when I contrasted my mother's life with her sister's, I knew which life I preferred so I didn't even hesitate to have children right away. This is an example of what I mean about observing the lives of others and drawing conclusions.
The women around you aren't much different from the young girls you know. They are only older versions. Observation will help you also to know what kind of man you should be as you observe other men in their marriages, and which behaviours work out for the best. Is your girlfriend anything like any of these women, and how do things seem to be working for that family?
"Be absolutely sure to look at what kind of a woman her mother is." This advice comes from Uncle Ben, who says he *always* looked at the mother! He swears by it.
If you conclude this problem is unchangeable; frequently causes trouble between you; is something you can't stand to live with; you can't alter things to cause it to change; and you understand that it could get a lot worse through being used to each other, and even, (heaven forbid!) -- taking each other for granted in marriage; then you should at least take a break from each other, and each go out with other people. Don't see each other at all until the set time is up. Then, if you still want to, you can assess the problem again. If nothing has changed you should stop, regardless of "obsession" and present pain. "Short term pain for long term gain", you know!
Right now you may be holding your life and future happiness in your hands. If things add up wrong you'd better run away, no matter how obsessed you are. Obsession and passion can never last through marriage and stressfi; times that are sure to come, as they always do. You need to always be able to work together for your common good. Do the best you can to choose a life you can live with cheerfully and in contentment for years. If you can't get over this; can't discuss and overcome it; can't cooperate about it; and your ideas and ideals of life differ; get out completely. Right away.
Beauty, youthful charm and passion won't last as you are experiencing them now, and for either of you. You need a much firmer foundation for a happy, lasting relationship. Now is the time to make the best of your chance for a good life.
Caring good wishes, Mary