Pinescript variable doesn't change its value

Question

So I have a problem, thought a lot about it but not able to fix it so I would appreciate some help from you.

To make it simple, I'll give another piece of code.

currentRSI = ta.rsi(close,14)

var tradeExists = 0

if (currentRSI > 50 and tradeExists == 0)
    tradeExists := 1
    alert("Long trade")

In my case, if currentRSI crosses over 50, so it gets to 51, AND in the same candle of the timeframe it gets to 49.5, the tradeExists value will remain 0 but the alert has been sent how could I fix to detect that and close the trade, any idea if I can do this?

I want to specify that I also tried using varip tradeExists = 0 but the variable still gets rollback at the close of the candle.