Why doesn't {in love with} fit in the sentence: When I was a teenager, I fell _____ this Italian guy [closed]

My answer was {in love with} but it was marked wrong.

Yet Cambridge Dictionary uses a very similar example in their entry for fall in love

• He fell in love with a young German student

Can anyone fill the gap and explain why theirs is the correct solution but mine {in love with} isn't?

When I was a teenager, I fell _____ this Italian guy. I was so in love that I spent all my money on a ticket to Rome

P.S This is not a request to proofread, I have clearly identified the problem that is making me confused.

Solution 1:

When I was a teenager, I fell head over heels with/for this Italian guy. I was so in love that I spent all my money on a ticket to Rome

To fall head over heels (in love) with or for someone is a common-day English expression which Merriam-Webster says is also an adverb. It means to be so much in love that you are prepared to do crazy things such as spending all your spare cash on a one-way ticket to Rome. In other words, the person's life is figuratively turned upside down.

Vocabulary.com has a good description and explanation

When you're head over heels, you're confused or thrown off by something. People say they're head over heels in love when they feel disoriented and swept up by their romantic feelings.

You can use head over heels for a particular state of disarray, although it usually shows up in the context of love, and it's come to mean something closer to "extremely." Your parents are lucky to be head over heels in love after being married more than twenty years. The original phrase was "heels over head," which makes sense, since our heads are normally over our heels. For some reason, it was reversed to head over heels in the eighteenth century.