Who is in your heart and in whose heart are you in? When we love someone, we want to fully enter into the heart and life of our beloved and we want our beloved to fully enter our heart and life. But in reality it doesn't happen with the relationships of this world. This is possible only in our relationship with Krishna because only He is selfless in His love and capable of satisfying us fully. Therefore Krishna says in Srimad-bhagvatam 9.4.68 -
"sādhavo hṛdayaṁ mahyaṁ
sādhūnāṁ hṛdayaṁ tv aham
mad-anyat te na jānanti
nāhaṁ tebhyo manāg api"
"The pure devotee is always within the core of My heart, and I am always in the heart of the pure devotee. My devotees do not know anything else but Me, and I do not know anyone else but them."
Rather than trying to give our hearts fully to the people of this world and being frustrated is to give our hearts fully to Krishna and never be frustrated. Therefore, it is best if we give Krishna a place in our hearts and thereby occupy a place in His heart. This is true wisdom, maturity and success of life.