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My boyfriend will buy two return tickets in Mexico to travel to the UK. One for him to travel to the UK and back to Mexico, and one for me (I am already in the UK) to travel to Mexico. Is it possible for me to use the return ticket that he buys me as a one way, or am I not allowed to do that because I haven't actually come from Mexico to the UK and back to Mexico again? Am I able to travel to Mexico from the UK (on the return ticket that my boyfriend bought for me, using it as a one way ticket) if I haven't actually flown from Mexico on it?