Pain of Love is the first stage in Lovesick Again.
The stage begins with 1 HaterBaa 2.0 which spawns at 3.3 seconds100f.
When the enemy base is at less than 99% HP, HaterBaa 2.0 will spawns every 1.3~2.7 seconds40~80f, which stops after 15 HaterBaa 2.0s. A debuffed Baa Baa appears as the boss. Baa Baa spawns every 4~8 seconds, which stops after 5 Baa Baas spawn.
As you may have inferred (or maybe not) HaterBaa is a Metal enemy. It has a pathetic 10 HP, but there's a reason this is an Expert Stage - it deals a whopping 13,500 damage, so bring at least three meatshields. The stage spawns 15 of them after you hit the base, so bring Critical Hit Cats like Jurassic Cat, Space Cat or Rope Jump Cat.