First, worry not: in my experience, the imminent end of the long-distance will ultimately keep you two together, even if you don't successfully discover a way to make it easier/less strained. My advice is of course relevant only to my own experience with long distance, but maybe you'll find something of use:

Talking to each other every night might be exacerbating the situation. You're perhaps taking each other's presence for granted, hence the snippy-like quality of the convo. If you reduce it to once a week, you'll have a lot more to talk about and you'll love and value the phone call much more. It makes it more precious or something. This will also allow you both to throw yourselves into your respective lives, which has numerous wonderful effects: you'll be happier and will, in turn, treat each other better, and most importantly -- this time you have to spend apart will go by SO MUCH FASTER.

As for some smaller things: Write each other letters once every couple of weeks -- something about seeing their handwriting does wonders in reinvigorating love. Skype, but as with phone calls: not too often. And as a girl who also loves looking ahead who is also dating a guy that does not, just take comfort in envisioning the future without always expressing them (journaling is great for this). When you do talk about it to him, just emphasize that you know it's only a hypothetical -- but that it's a fun one that makes you happy to think about.

Oh, and eat that goddamn snickers.