Definition of Love according to Rupa Goswami

The pure spiritual love is the innate attraction of the soul for the Transcendental Lord.
Krishna Das Kavi-raja Gosvami writes in Caitanya-caritamrita (Madhya lila 22.107):

nitya-siddha krishna-prema sadhya kabhu naya
shravan-adi shuddha-citte karaye udaya

The eternal and perfect love for Krișna - nitya-siddha prema kṛṣṇa
cannot be attained from anywhere else - naya sādhya kabhu
The heart is purified (and the perfect Love for Krișna ) is awaken - citte śuddha karaye udaya
beginning with Hearing (the pastimes of the Transcendental Lord) - ādi śravaṇa

The meaning is that spiritual love is a potential in the heart and when the soul is cleaned
of the dirt of material attraction, which covers the soul,
one attains the state of pure Virtue - shuddha sattva, and in this state,
as one practices Saddhana Bhakti,
beginning with Hearing (shravan-adi) the pastimes of the Transcendental Lord,
 and the rays of spiritual love appear "on the horizon of the heart",
as Rupa Gosvami explains in Bhakti Rasa-amrita Sindhu (1.3.1):

śuddha-sattva-viśeṣātmā prema-suryāḿśu-sāmyabhāk
rucibhiś citta-māsṛṇya kṛd asau bhāva ucyate

The (love's) specific state of the soul - atmā viśeṣa
in pure virtue - śuddha-sattva
as the rays of spiritual love are manifested - prema-surya aḿśu sāmyabhāk
and the heart is melted by the (love's) tastes - citta rucibhiś māsṛṇya
is called the Beginning of Spiritual Love - kṛd asau bhāva ucyate.

This Bhava is not the result of sadhana bhakti.

As one continuously do shravan (hears about the pastimes of the Transcendental Lord),
kirtan (praising the Name, forms and qualities of the Transcendental Lord)
and other limbs of Saddhna-Bhakti, one cultivates
the Desire to detach oneself from this world and
to get closer to the Deity of one's heart.

When saddhana-bhakti attains maturity,
all undesired qualities and attractions are removed from the heart of the Sadhaka (practitioner).
At this time, through the mercy of the Transcendental Lord or His devotees, appears bhava -
the state of budding of spiritual love - in the clear heart of the sadhaka.

When this Bhava
1. melts even more the heart, much more as in the beginning state of spiritual Love,
2. the feelings of transcendental ecstasy increase exceedingly
3. and a deep feeling of mamata (possession) for Krishna arises,
then this state is called Prema - Spiritual Love.

Srila Rupa Gosvami defines Prema in his book Bhakti Rasamrita Sindhu (1.4.1):

samyaṇ masṛṇita-svānto / mamatvatiśayaṇkitaḥ
bhāvaḥ sa eva sāndrātmā / budhaiḥ premā nigadyate

The state (when) one's own (love) Nature melts further, - samyaṇ sva anta masṛṇita
the desire to possess (Krishna) marks one - atiśaya mamatva aṇkitaḥ
and Bhava becomes more powerful in the soul - bhāvaḥ sa eva atmā
is called by the intelligent persons Prema - budhaiḥ premā nigadyate