My friend's on an F-1 student visa in the US. His girlfriend's from a Visa Waiver Program country, which grants visa-free entry into the US for a maximum period of 90 days per stay. My friend has searched high and low for a maximum amount of times per annum that a person can enter the US without a Visa under this program - he has never come across a limitation, and thus believes that if his girlfriend comes over, stays for 89 days as a tourist, takes a trip to Canada and returns Stateside, she's got another 90 days of being in the US legally, as a tourist. He's convinced that she can do this a number of times and therefore live with him whilst he studies, but I can't help thinking he's overlooking something critical and crucial that rules what they are planning on doing out. He's on a scholarship and has considerable savings, so work isn't an issue for either of them for this yearly period...is he right in thinking he can go ahead with this plan, or it somehow illegal?