"I have booked a flight to Warsaw on Thursday, but she says she might be busy that weekend, so good job it was only a low cost airline."
Oh man I hope I'm wrong but that doesn't sound particularly positive, " she might be busy?" to busy to be with you. Ah Dude, man that doesn't sound good at all.
Hmm. Listen don't come on to heavy towards here if she acts cold and distant when you are in Poland. DON'T GET ANGRY OR VISIBLY EMOTIONAL, when a woman see's a man act like this, two things happen. 1) they gain the upper hand and 2) Emotionally turbulent males are VERY UNATTRACTIVE.
Being cool, real cool is the best defense. If for example on your first day of arrival she acts up, ignores you or generally is behaving normally. Tell her you don't want to crowd her or force her in any direction. Get her to order you a taxi to the hotel in town, so she knows the details of where it is and where to contact you. Then go out and party really ******* hard. if she doesn't contact you whilst you are there return to England, lick your wounds and get into some hard work for hard currency.
If on the other hand she contacts you then she means she needs to talk. If all goes well scratch the idea above, if not carried on as outlined.

Man I'm now 31 with a missus of 5/6 years, during my early 20's (probably as half the older males on the board can testify) I had a relationship of 4 years which turned sour and another of 1.5 years. Unfortunately life is a learning curve and sometimes you are someone else's curve, leaving you with an unexspected lesson.
Look on the brightside, we could all die tomorrow so appreciate what you have while you have it. When its go **** it and move forward.