don't understand if you're saying you've been dating long distance for 3-6 mths or if you'll be separated from each other for 3-6 mths. if dating for that period of time, i suggest that you enjoy the long distance communication but keep you a nearby relationship or continue dating others as well. but, if you're saying that you'll be separated for that long, then i suggest you keep the communication flowing and remain patient and reassuring. also wanted to add that if you happen to be the person remaining behind, don't stress the other out with worries, insecurities, or arguing. it only seems to push the other further away and it's not like they could drop everything and come back right away anyway
After my girlfriend (now wife) left university she lived in a different country with her mother for about 1 1/2 years, before moving back to move in with me. Keep communication going - it's old-fashioned but writing frequent letters is nice, it's somehow more special than getting an e-mail. Phone calls as well, and if you are both into it phone sex is better than none ;-)
Keep yourself busy, so you are not thinking of each other and how much you miss each other too much of the time. This will also help avoid the temptation to stray while your partner is not around! Don't even be tempted by that, even if it is impossible for her ever to find out, it'll mess with your head in a way that isn't healthy.
I really do not think Long distance relationships work to well unless it is a marriage, and then you will just have to work hard on maintaining it luck jo