Question

I think he will run into his ex-girlfriend but he won't care.

Answer 1

Answer:

I think he will run into his ex-girlfriend, but he won't care.

Explanation:

The given sentence is a compound sentence, as it consists of two independent clauses:

• I think he will run into his ex-girlfriend.
• He won't care.

These sentences are connected by the coordinating conjunction but. Coordinating conjunctions that connect two independent clauses are always preceded by a comma, and that's why there should be a comma between the words ex-girlfriend and but.