You probally looped the function.
Idk how you want it but heres an example if you press crouch and melee at the same time:
thread onplayerspawned()
self thread spawnSlideBind();
spawnSlideBind()
{
for (;;)
{
if( self stanceButtonPressed() && self meleebuttonpressed())
self thread spawnslide(); // <- obv your slide code then
}
}