The liars game is a big drag. I see on this web site that a lot of people give veryshort responses that may or may not have much merit. In fact, I think many of them are scarcatic jack off type comments.
Your concern, however, has caught your attention. Honesty is most important in any relationship. The way I measure that is with continuity. If someone demonstrates what they say, then all is well. When there is lack of continuity (for any reason) red flags go off in my head!!!!!!
It sounds like your partner has not demonstrated what he said he was going to do. Perhps he means well and he's lazy. Perhaps he's waiting for the last minute. Perhaps he's a procrastonator by habit. Perhaps he's lying. It's hard to acuse someone of being a liar, when in fact, his behavior could be based on a number of reasons.
What is important to you, however, is you are noticing his inconsistency. There are a number of questions you may want to ask yourself. Why is this important to you? Is it the money? The trip? His loyalty to you? Or your values? Perhaps your values in your life place high regard for continuity of words and action. I belive they must match.
You might want to take note of how you feel about this charactor trait with your partner, and see if he does this in other areas of his life as well. Perhaps he's not the guy for you. Or perhaps it's a faux pas issue that goes along with other meaninless neuances.
Good luck to you.