What does "heart's release by love" mean?

Loving-kindness (or love in this context, though piyo might be more appropriate for how native English speakers normally use the word love or just like) is the first of four brahma vihārā or the Four Immeasurables (see below). And so to meditate, contemplate, make vehicle and road one's mettā is usually first and foremost in any aspiring Buddhist's set of practices. Alongside related behaviors and beliefs, like thoughts of good will and mindsets of harmlessness.

Habitual anger and hateful thoughts, speech, and deeds tend to be the most immediately destructive form of unwholesome action. And so for most of us, first on the chopping block should be our malice and cruelty. The most effective antidotes to which is cultivating the likes of loving-kindness, good will, and helpfulness; accruing merits or "good karma" in popular terms; and fulfiling pāramitās for more fortunate (bright) future births conducive for Dhamma practice.

After mettā, the next three brahma vihārā (also known as Divine Abodes) are:

Karuṇā: compassion; taking pleasure in actively helping others; wise empathy; kindness towards the unfortunate; sympathy for another being's sorrows.

Muditā: sympathetic joy; taking pleasure in others' successes; happiness (for); appreciation for another's welfare; the antidote to jealousy and envy.

Upekkhā: equanimity; mental balance; lack of reaction; composure; settling in dispassion after becoming disenchanted from worldly existence and sensual desire. (The Mahātherī Sumedhā is one of my heroes, a most inspiring Noble Friend!)

As an aside: it's when I finally made some headway (though still far to go!) into handling my lifelong bad habits of a hair-trigger temper, grudge-holding, and disproportionate vengefulness, is when greed reared its ugly head in a big bad way! So now to avoid more bad-mood impulse buys (I would have gotten along just fine with a phone 1/8^th the cost of this shiny toy...) and... more other appetites... I now divide my meditation between developing mettā (like recitations and meritorious deeds) and cultivating asubha saññā. (The sense of the worthlessness and danger of both sensory pleasures and worldly values, not watching autopsy videos or whatever.) Must be a good sign that Kilesamāra, Death God of Delusion and Defilement (kilesa) is doubling down his efforts into keeping me snared, now presenting subtle temptations and laying out trickier traps. So now I must be triply-vigilant to lock my door when the devil knocks and offers me candy.

In any case, for emphasis: the Buddha's definition for meditation (bhāvanā) is bhāvitāya bahulīkatāya or to use what is learned frequently and live by it.

There's nobody here, only the ardent amateur struggles to keenly pursue and heartily hold the beginning of the heart's releases.