How to write Character A dialogue with Character B's reaction in the mix?

Hello!

I want to write a scene where Character B thinks Character A is going to confess their love and show Character B getting their hopes up...

Like this:

"I love," Character A says.

Character B's heart skips a beat.

"Your bum," Character A finishes.

What's the most concise way to write that?

I'm guessing it's incorrect to go:

"I love," Character B's heart skips a beat, "your bum."

Please help me, I don't know what to do!! Thanks!