Love is an experience of a relationship, it is not an 'experience object' by itself. Like when you have a rare pleasurable experience, the projected relationship towards this 'Pleasurable experience object' is love. Love is a projection from you towards the manifest experience. It is the highest projection you are capable of towards the manifest. It is the highest vibration your reality could vibrate in. It is something projected by you towards the manifest object. So the source of love cannot be anything other than you since it is you who projects it onto 'experience objects'.
Conventional love:Conventionally, our belief structures filter what can allow you to open this projection onto the manifest. Such a case, would be conditional love. So when the 'experienced object' is passed through your belief filter, and is deemed worthy of the experience of love, then you shine/project love on to the 'experience object'.
For example, a teenager who is extremely eager to try alcohol for the first time in his life comes with very high expectation. If the right amount of alcohol is given to him, he would shine projected love towards that inebriated experience. Whereas, a devout christian who is deeply against the concept of alcohol may process this experience in an extremely negative way. So we conditionally open and close our love projection based on the interpretation of our belief matrix and whether or not it interprets the present experience to be worthy of such a lofty projection.
In such a case, the love is dependent on the existence of the 'experience object' and is also dependent on the belief structures interpreting the stimulus as worthy of love. So if either of them changes, the 'experience object' or your 'reality input interpretation/belief structures', your projection would change into something else (not love anymore). Then your vibration may lower into other states and once again there would be a need to seek a manifest object that would pass through the filter and allow you to experience this love again.
About the belief filter and the fleetingness of conventional love:This 'belief filter' that conditions your projection potentials is the prison. Also since both the 'unconscious belief matrix' and the 'manifest experience' are continuously changing, the experience of love is inevitably fleeting. The freedom lies in transcending this matrix and shining the light of awareness on all gross and subtle beliefs that form this matrix like prison.
About transcendent love:Now, I've used words like prison, matrix, unconsciousness, fleeting, inebriated, dependence, lower vibration whose connotations point to negative phenomena. I've also used words like highest, transcendence, freedom, light, awareness where the connotations point to something very positive. The transcendent love however includes all of the above including the negative phenomena. In fact negative/positive distinctions are only based on the interpretative framework and duality. The transcendent love is for all interpretative frameworks, all of manifest experience, all its potentials etc. There is 'Nothing' literally that is not embraced by transcendent love.