Love the one you're with

"To take your pleasure where you find it"

What are the origins of this phrase?

I don't know the origin but your phrase sounds like someone trying to explain CSN's "Love the One You're With":

Dont be angry
And don't be sad
Just keep smiling
And thinking about all the good times that you had
Cause there's somebody right next to you
And they're just waiting for something to do

Theres a rose
In a fisted glove
And the eagle flies,
Flies with the dove
And if you can't be with the one you love,
Then love the one you're with
Love the one you're with
Love the one you're with

The anthem of the 60s. All together now -- sing!