Zero. Nil. Nada. Zip.

The only time this kind of things raises a red flag, to the best of my knowledge, is if you repeatedly book back-to-back trips (this is discussed in MANY places here, but in brief it means booking two round trips and using one portion of each in order to avoid a Sat. night stay). You are in a different situation - buy the ticket and don't think twice about it. Keep in mind that once the plane for the return trip departs with him not on it, you cannot recover that ticket or reuse it (not that you would want to - $100 fee if you decide to use it later for some reason but must decide before the plane leaves....).