These are a list of some Valentine's Day-related idioms as well as their respective definitions and a picture that matches the idiom. I use this style of activity anytime I have students interested in learning idioms and it always goes over very well! Basically, I print and cut out the phrases and pictures, then ask students to match the idiom with their definition and picture.
For a small class size, I scatter the phrases on a table and let students work together. For a large class size, I put the definitions and pictures on the board with some magnets and then pass out one or two idioms each to small groups. Students should put their idiom on the board next to their definition and picture when they think they know the answer.
I provided the answer key and a worksheet here, though I think the worksheet is probably too much writing. Usually I just provide the answer key to students and allow them to take any notes on the worksheet as we discuss each idiom.
This activity is for higher level students that can understand the meaning of a phrase using simple English in the definition. I think it's especially good for eikaiwa-type groups, but I have used it in a high school classroom as well.