expression, ichidan verb
two-time; play both sides; sit on the fence
Refers to dating two people at the same time without their knowledge, or more broadly to hedging one's bets or being noncommittal. The romantic sense is the most common modern usage.
See also: 二股をかける
彼は彼女と別れずに他の人とも付き合っていて、二股かけていた。
He was two-timing, seeing someone else without breaking up with his girlfriend.
どちらの案にも賛成しているように見えて、彼は二股かけているだけだ。
He seems to agree with both proposals, but he's just sitting on the fence.