Maybe it is not a good idea to lend your bitcoins to someone. Your idea of investing your bitcoin in gambling, by putting your money on the house. You know it will grow because the house always win in gambling. YOu just have to pick a good gambling house, the one with a lot of gamblers going in.
If gambling house alone always win means, there will not be an industry in the name of gambling as there will not be any chances to win for gamblers all the time.
I mean to say, even gambling houses also do face losses time to time when some professional gamblers win. So, picking a perfect gambling houses alone will not remove the risk part of investing into gambling houses.
Still, it s a good way of growing bitcoins but definitely it too has some risks.