It sounds like you may be allowing yourself to over think this whole thing.......7 months may seem like a long time but in reality it really is just a drop in the bucket. Right now you should just be living this relationship instead of trying to determine if it will last forever. 23 isn't very old to be thinking about forever!
It looks like you are trying to force your feelings and there for are causing yourself stress and anxiety. Often when we talk about the future, or try to plan for it when we really are not ready we cause these kinds of fears to come out.
Forever is a very long time, and while it would be wonderful is we could know if someone is the right one within a few months, the reality is it often takes years to develop the kind of relationship with another person before we know if he or she really is the one we want to spend the rest of our lives with.
A lasting relationship is never built on the lust and attraction you feel right now, a lasting relationship is one that is built on trust, honesty and compromise. Many people fall into love and get married......and of course they think it is going to last for ever, why else would they marry? But the truth is a lasting relationship is built over time and with the effort of both partners. You can have all the love in the world, you can be perfect for each other..........but in the end if both of you are not willing to work together then the chances of it lasting are slim. And that is why we see so many marriages end when times get tough! Few are really prepared for the reality of marriage and family and most simply assume that since they love each other things will always work out. Then when the marriage hits some speed bumps they assume its because it was never meant to be, and end up giving up.
The key is getting to know each other and just living your life, when the time comes be prepared by discussing what you really want in the future. And I am not talking about how many kids or how big of a house, you should discuss the important things in a marriage such as how to handle stress, what you expect out of him and what he expects out of you. Then you can both move into the future with your eyes wide open and be prepared to work for your relationship.........if you can not communicate and work together then it will be harder, but if you work together you will make it.
Stop over thinking it.......right now its time to get to know each other and just live your life. In the end if you love each other, and are both willing to work together then you can both make anything you want out of your life.
Of course you can.........if you did not have some kind of panic or doubt at 7 months I would tell you that you were in denial!
The fact is its so early in your relationship and when your thinking about forever your natural defenses are kicking in and questioning everything because its to soon. That is perfectly normally human behavior.
We all tend to have doubts about our partners early in the relationship, its natural to have a slight distrust of people because you are feeling so much so quickly. Now if there is a reason for these feelings, such as something that he is doing that brings it on then you have a valid reason. But if there is nothing there, then it is safe to say that these are normal feelings and over time you will be able to relax more and enjoy what is to come.
Another thing I want to bring up......do you often get panicky over new things? Or allow yourself to stress over everything? If the answer is yes then you may be more prone to anxiety and this is something you may want to discuss with your doctor. The fact is sometimes we are all a little more prone to anxiety and often slight changes in our lifestyles can help us.
If this is the only thing you are anxious about then it is unlikely to be any medical issues, but I did want to bring it up on the off chance.