The third alternative is correct (C).
You have to use the comma and but.
There exists between the two periods of the stretch an adversative condition, where the terms like "but" or "however" should be used.
The central idea suggests that talking to someone is good, can help relieve the symptoms of a love conflict. However, regardless of the help obtained in a conversation, when the rational feeling is present, the situation is actually resolved.
That is, the term "but" contrasts and connects the two periods that form the phrase.
A talk with an older friend, sibling, or parent may ease the symptoms, but first loves usually subside when rational thought returns, whether or not you take someone's advice.
