I see this one as a feeling of uselessness in a relationship, the pain of not being able to cheer up the one person you love the most, and guilt the speaker feels for not being able to do so. The two get along great when the speaker's partner is in high spirits, but the speaker knows that this happiness is fleeting, hence their love / connection being "almost true". They almost get along, things almost work.
I see this one as a feeling of uselessness in a relationship, the pain of not being able to cheer up the one person you love the most, and guilt the speaker feels for not being able to do so. The two get along great when the speaker's partner is in high spirits, but the speaker knows that this happiness is fleeting, hence their love / connection being "almost true". They almost get along, things almost work.