Hi :-D
What does it mean when you say "I wanna get all sentimental"? [STRIKE]?[/STRIKE]
It's not something I would ever say, but if I heard it, I would understand it to mean "I want to feel sad or tender about the past, or to feel nostalgic, about someone or something".
Remember that "wanna" is not correct written English unless you are directly quoting someone who actually said "want to" so that it sounded like "wanna".
Thank you, emsr2d2 so much :-DAh, song lyrics! The bane of our lives. Bear in mind that song lyrics are frequently ungrammatical. Song writers choose words which rhyme or scan or fit the rhythm of the music. They don't think about grammar when writing songs.
Having said that, there's nothing particularly ungrammatical about this particular line. I guess it just means "He's a special person and when he looks at me, I want to be all soppy".