There's a bluebird in my heart that wants to get outbut I'm too tough for him,I say, stay in there, I'm not going to let anybody see you.

This quote is about not allowing your emotions to be seen by others. The bluebird in the speaker’s heart is a metaphor for their emotions, which they are suppressing and not allowing to be seen. The speaker is speaking to their own emotions, saying that they will not let anyone see them. This implies that the speaker is feeling vulnerable and may be afraid to show their emotions, so they are tough and not letting anyone see them.