晴れる: a clearing sky and feeling relieved
Read 晴れた with 空 and 気持ち. Separate rain stopping before noon from the sky clearing in the afternoon, and distinguish feeling relieved after speaking from having every worry resolved.
Rain stopping and the sky clearing
晴れる（はれる） can mean to clear up. 「昼前に雨がやみ、午後には空が晴れた。」（The rain stopped before noon, and the sky cleared in the afternoon.） 昼前 locates the rain stopping, while 午後には locates the sky clearing. The sentence gives two changes at different times.
晴れた is the past form of 晴れる in 空が晴れた. 空 identifies the weather sense. Follow each subject and time expression rather than treating the rain stopping and the sky clearing as one simultaneous event.
Relief after speaking to a friend
晴れる can also mean to feel relieved. 「友人に悩みを話したら気持ちが晴れた。」（I felt relieved after telling my friend about my worries.） 気持ち is what changed here. The sentence reports relief after telling a friend about worries.
話したら links speaking with the following emotional change. 悩み is the content shared, and 気持ち is what felt relieved. Sharing the worries and feeling relief do not add an action in which the friend solved every problem.
The subject identifies the sense
Both examples use 晴れた, but 空 and 気持ち identify different senses. A sky clears in the weather example; a person's feelings become lighter in the other. The same past form need not describe the same kind of change.
The first sentence separates two events through its time expressions. The second links relief to speaking through 話したら. Read the stated emotional result without replacing it with a change in the sky or a complete resolution of the worries.
In 「友人に悩みを話したら気持ちが晴れた。」, what felt relieved, and does the sentence establish that every worry was resolved?
Show the answer and why
気持ち, the person's feelings, changed. The person felt relieved after telling a friend about the worries. The sentence describes neither the sky clearing nor every worry being resolved.