how long can it last?

It's probably a little of both. He wouldn't go to that much trouble if he didn't love her, but the distance would also make it easier for both of them to get along since they won't be rubbing on each others nerves day to day. That doesn't mean they couldn't live together 24/7, it just means they haven't tried it yet. The good thing is that they would have a good base to build on when they finally did end up living closer to one another. Really, the only way to know is to wait until it happens. I'm sure they're discussing the big issues so they should know if they would be clashing all the time on the small stuff. (How cold the room should be, what channel the TV should be on, what kind of music is playing around them, etc.) In the meantime, enjoy the time you have together.

might be so she dont git on his nerves but traveling that far to see her also could mean he is really in love with her .Have they talked about marraige or anything like that?

I'm not sure about it. These days, who knows why people do what they are doing. I think he could possibly care for her. He could also just be using her once a week. He may have anohter girl or a wife. I would tell her to ask him why he doesn't come over to see her more than one time per week. He may not be very interested in having a serious relationship or something. That is a good possiblility. He may think that if he comes over moreoften, he will be in a committed realtionship. I would have to ask him, myslef, why he doesn't see me more often.

Relations like this one are generally fragile, IMHO. Sooner or later one of the partners will try to meet somebody else. It is true that some guys are independent and find this kind of relationship fulfilling. Girls, tend more to look for security and a stable relation.

Well, only the girl can tell for sure. But based on your post, I believe that the guy loves him. I don't think that he just like to be away from her more because he still exerts his efforts to be with the girl. And I think that even couples need some time away from each other and I think that kind of space is healthy. I think that if the guy doesn't want to be with her that much, then he should've let her go in the first place.