won't vs. want

I can't tell "won't" from "want" in hearing.

I know those phonetic signs are different and even can pronounce both words individually. But, when I hear what somebody says, I can't distinguish them.

For example, a friend of yours came to your place and said,
"I won't stay long." "I want to stay long."

Those have entirely opposite meanings.

He/she says "I won't stay long", but I answer, "sure! you can stay as long as you like".
It can happen.