I suppose the first thing is trust. In my case, my gf came with me a few times and got to know the people I knew in the other locations. That put her mind at rest. Also I took care that I always had my mobile with me and on so she could call at any time. I think there is nothing worse than becoming careless and letting your battery run flat and meanwhile you're partner can't get through - causing her to wonder what you're up to. It depends a bit on her social life and where you go - but if you're a western guy and spending anytime in infamous cities (eg Bangkok) you can be sure what her friends are telling her. So if you take steps to head this off and everything you say "just adds up" in her mind then at least the trust thing won't be a problem. Try to involve her in your work a bit - ie telling her about your meetings, what went well and what didn't. Then she will be more apart of this part of your life.

Next issue is just the time thing. Just try and set aside some time when you're back. I think even non travelling couples go through periods of not seeing each other much because of long work schedules. If you're travelling alot - especially over weekends it should be possible to have extra time off to compensate. If its really that difficult, you need an end in sight - eg "the next 6 months will be impossible, but when the projects finished then I'll be based here for a while".

Looking back I don't think I've ever had a relationship fail because of the travelling thing. Usually that was just a catalyst for what was going to happen anyway. Maybe you should consider whether the problem really is just the travelling.

And... if all else fails.... (I sincerely hope it doesn't)... find a woman that travels alot too. After a break up I met a purser with an "international airline" and obviously she was travelling all the time. It was great fun sitting around planning schedules and rendez-vousing in different locations.