The word describing a person practising such behaviour is promiscuous.
1: having or involving many sexual partners : not restricted to one
sexual partner or few sexual partners
I suppose I was quite promiscuous in my youth.
It's a fallacy that gay men are more promiscuous than ...
Perhaps this old saying describes the situation.
They are trying to teach their grandmother to suck eggs.
Teach your grandmother to suck eggs.
to give advice to someone about a subject that they already know more about than you. Cambridge Dictionary
There's a difference between mansplaining, mentioned in one of the comments, and the above saying.
A day late and a dollar short
Too late and too feeble to achieve the desired effect.
His apology was a day late and a dollar short.
The subject of the idiom did something, but it was inadequate. It originally referred to paying the landlord for the rent not enough money and after when the rent was due.
How about playing the field?
to hold an interest in a number of people or things, especially to become romantically or sexually involved with a number of partners
This is an informal and fairly neutral way to put it.
The opposite would be committed:
Definition of committed relationship: a serious and lasting romantic relationship with ...
This is not an idiom per se, but I'd say:
I really dig something.
The verb 'dig' is defined in this learner's dictionary as:
a [+ object] : to like or admire (someone or something)
I really dig this music.
"Missing the window of opportunity," maybe?
Here's a link to window of opportunity on Wikipedia, which has this to say:
A window of opportunity (also called a margin of opportunity or critical window) is a period of time during which some action can be taken that will achieve a desired outcome. Once this period is over, or the "window is closed", the ...
According to this source the rather graphic words "spit" and "moisten" are possibilities along the standard "drizzle".
Here is an instance of use of "started to spit".
From this other source you can select more terms that connote the idea in just as graphic a fashion.
sprinkling, spraying, spritzing, peppering, dusting
mizzling, (intransitive, now ...
That's my jam.
It's not just for music anymore. That's not really debatable. (See related question on ELL.)
Kids totally know about jam (that is, my jam), big time.
(For more on my jam, see Urban Dictionary.)
Perhaps sprinkle could work for you?
("it sprinkles", "it is sprinkling", etc.) North American [no object] Rain very lightly.
‘it began to sprinkle’
In your example, it would be:
There was a light breeze blowing. Timid clouds gathered around and then it started to sprinkle.
The idiom in the doghouse can apply in this situation:
In trouble with someone due to one's misdeeds or blunders.
I'll be in the doghouse if I come into work late again this week.
You've been in the doghouse with Maria ever since you forgot her birthday.
The Free Dictionary by FARLEX
The question is about a word to describe men and women who want to have many different sexual partners. It might be useful to look at synonyms for voracious appetites.
Such sexual athletes might be avid, insatiable, rapacious, ravenous or gluttonous in their unquenchable pursuits of the opposite yet slower moving sex.
I agree with Edwin's answer based on Cambridge Dictionary's definition. A more extreme form would be a combination of kill and success. In the question's example I would conclude with a straightforward success killed them.
Some useful expressions from American politics:
"Malarkey" is an Irish-American slang word meaning "bull*" (Urban Dictionary).
I wouldn't recommend actually using this one.
This is a common expression, and can be used as follows:
Hey, straight talk, what's your opinion about "x"?
Another expression that's worth mentioning ...