Reeeeka, don't feel like you're being a b*tch about this at all--I'd be upset too! (A friend of mine just had a major gaffe with money and I feel like slapping him with a big rotten fish right now...)
This will be an important lesson for both of you I think in boundaries and priorities within a relationship. So many people I know are very fly-by-night when it comes to money and live for the moment instead of living for longer-term goals and working towards them. In my opinion, how a person handles money and treats money can tell you a lot about how they respect other things in life, such as fostering relationships. I would hate it if it became routine for you to pay for tickets to visit--in the end, you may be out money you'll never see again but worse, you may feel your good nature has been taken advantage of.
I'm not so sure I'd pay for his ticket, either. He has to learn that the consequences of him not saving up for this trip could deny him the happy chance to spend time with you, and for me, that chance would be a pretty darn strong motivator to save up. It's not really that hard...for example, by just banking my spare change and limiting the number of drinks I have on the weekends when I go out, I can find 40 or 50 dollars in a month. Multiply that times a few months, and...you get the idea! And my friends cannot wrap their heads around that!!
we paid for our own airfares but whoever was the host paid for most of the outings and expenses during the stay.
This is an excellent plan and is something my friend and I always do. We will also alternate paying for meals, and if I'm hosting, always pay for the last meal we have together, which we try to make special.

In any case, I wish you the best, hope something works out!!