Date Airline Destination Seat Mate
April 2nd WTA Airways Chicago Doctor
April 9th Fly America San Diego Teacher
April 16th Air Express Atlanta Sports Coach
April 23rd Skyways Boston Attorney
April 30th MidUSA Air Seattle Ballet Dancer
The trip to Atlanta (1), the trip where Matthew sat next to the ballet dancer (3), and the trip where Matthew sat next to the attorney (7) were among the last three trips [April 16th, 23rd, and 30th (intro)], and the trip to Atlanta wasn't the one where he met the ballet dancer (6) or the attorney [he flew WTA Airways exactly two weeks before the one to Atlanta, and he flew Fly America exactly two weeks before he sat by the attorney (7), so, these three are separate flights, in some order.
He didn't sit by the teacher on the trip to Atlanta (1), so the flight were he sat by the teacher was on one of the first two flights [April 2nd and April 9th (intro)], but it wasn't first [after WTA Airways](1), therefore, April 2nd flight was the WTA Airways flight, the one where he sat by the teacher was the April 9th flight, and the one to Atlanta was the April 16th flight, and he sat by the ballet dancer and attorney on the April 23rd and April 30th flight, in some order.
He didn't sit beside the sports coach on the WTA Airways flight (5) so that wasn't April 2nd, he sat beside the sports coach on the Atlanta flight [April 16th] and it was the April 2nd flight where he sat next to the doctor.
April 2nd [first flight, WTA Airways, doctor] wasn't to Seattle (2), Boston (3), or San Diego (4), that flight was to Chicago.
The April 9th flight wasn't to Seattle [after sports coach which was April 16th] or to Boston [after Air Express, which would have to be April 2nd, but WTA Airways was April 2nd (1)](3), so, on April 9th he flew to San Diego.
Boston wasn't the last destination (3), so it was his destination on April 23rd and Seattle was his destination on April 30th.
Boston [April 23rd] was before the one where he sat by the ballet dancer (3), so he sat by the ballet dancer on April 30th flight to Seattle, and it was on the April 23rd flight to Boston that he sat by the attorney.
Since he sat by the attorney on the April 23rd flight, then he flew Fly America on the 9th [exactly two weeks before](7).
He flew Air Express before the flight when he flew to Boston [April 23rd](3) so he flew Air Express on the 16th.
He didn't fly Skyways to Seattle [April 30th](5), so, he flew Skyways to Boston on the 23rd and his last flight that month was on MidUSA Air (intro).