My leisure travel with friends has never ruined a true friendship. If you and your friends are independent persons who don't need crutches and if you respect other people's space and they respect your space (including accepting quirks), then I don't see why travel would ruin friendship. Trust, power and communication issues are where most relationship problems occur; if you don't have such issues with the friends with whom you travel, then it's easier -- especially if proactively dealing with money matters -- which seems to reveal the hollowness of relationships and show what is "friendship" and what is friendship.