The 30-year-old, who has been capped 30 times by Wales, has branded his time at Wasps "a fantastic experience".
"I am really gutted to be leaving after a year because from a rugby point of view it's been a fantastic experience and I've loved every minute of it," Thomas told the club's official website.
"I did, though, completely underestimate how difficult it would be to be away from my three kids and my wife, who weren't able to move up with me.
"Travelling back and forth has been really tough and I am incredibly grateful to Dai Young and Wasps for understanding the situation I'm in."
Thomas joined Wasps from Cardiff last summer.