Is the word that inspired you a
As a lass I’d wait forever
Could refer to girls at bars waiting for someone to buy them a drink
And once it happened we mixed together.
Perhaps the drink initiated a conversation which led to a relationship, love / sex ("mixing together")
Lines got crossed,
Again not sure, but it could refer to excessive drinking leading to one of the partners "crossing a line" either verbally or physically
Love was lost.
Obviously it would have led to the end of the relationship, as drinking (or too much of it) often does.
And just as two becomes one,
A break-up would cause "two to become one"
One turned to none
Pure speculation, could possibly refer to suicide
And left the floor a bit wetter.
Most probably due to tears, the family / ex-partner crying about the loss.
Very speculative, I paint a dark picture with my explanations.
P.S. it fits hints 1, 3, 4. Maybe my wacky explanations are why it doesn't fit hint #2