What is 'Halving'?

The word halve means reduce to the half. In Crypto World isn't that diferent. The halving of coin is when the coin uses PoW(Power of Work[needs to be mined to keep the protection of the coin]) and the reward per block mined is trduced by half.

The Bitcoin Halving is supposedly to happen in May of this year(2020).

Is Bitcoin Halving already priced?

In theory when the halving happens, the price is suppose to rise. And what happened in the last Halvings.

But some experts think that the prior behavior is not going to happen in this halving.

We can't ensure nothing, we just can make assumptions about bitcoin halving. We need to wait and see that happens when the halving of bitcoin happens.

Should i buy bitcoin because of bitcoin Halving?

Yes,if you want to make some small profit. Even if the bitcoin halving doesn't make the value of bitcoin goes ridiculously up. In the long term we all know that bitcoin price will rise. The BTC/USD  it's just a price but Bitcoin is all an idea of financial independence. It's to you if you want to invest know just to make some profit for bitcoin halving or keep the bitcoin for a long more and probably make some more money.

How i can be always informed about when halving will happen?

Binance already has a page where you can see how many days it lefts until Bicoin Halving.

Binance Bitcoin Halving Countdown.