Here, rain becomes a way of saying what two people can't quite say out loud. The speaker imagines that rain exists to express unspoken emotion, and as it falls, the bond between the speaker and their partner deepens, even though very little is spoken. The walls both of them built to protect their hearts have come down, leaving them exposed but relieved.
The feeling is one of release. The line about no longer suffocating and finally being able to take a deep breath makes the rain seem like fresh air after a long, tense stretch. The clouds "set free" the couple's love, and the image of their bodies soaked in each other's tears blurs rain and crying together, so that sadness, vulnerability, and closeness all mix. The poem ends with a plain "I love you," which feels earned after so much indirectness. The mood is tender, quiet, and honest, like an exhale after finally dropping your guard.