Verspielt is the past participle of the verb verspielen, which means to lose something through gambling, frivolity, or playfulness. It carries a sense of having carelessly thrown something valuable away.
In the song, Wincent Weiss sings, "Hab' in mei'm Leben schon genug verspielt" (I've already gambled away enough in my life). He uses this powerful word to express deep regret over past mistakes and relationships he didn't take seriously, adding a layer of urgency and sincerity to his current proposal.
This song is one big, adorable, and slightly clumsy marriage proposal! Wincent Weiss isn't singing about grand, dramatic gestures. Instead, he's remembering all the small, perfect moments that led him to this point. He thinks back to the beginning of the relationship, seeing them in a "kleine Wohnung / Mit der Matratze auf dem Boden" (small apartment / with the mattress on the floor) and on long car rides where his partner is sleeping next to him. It's these simple memories that build the foundation for his big question.
He feels this pressure, maybe from friends or just from himself, telling him not to overthink things and to seize the day. So he decides, "Wenn ich jetzt nicht frag' / Dann frag' ich nie'" (If I don't ask now / I'll never ask). The proposal itself is so sweet and funny. He interrupts everything to ask, "Es tut mir leid / Hast du kurz Zeit / Mit mir den Rest deines Lebens zu teil'n?" (I'm sorry / Do you have a moment / To share the rest of your life with me?). He even apologizes for asking! He follows it up with a casual, "So fünfzig Jahre reicht / Bisschen mehr vielleicht" (Like, fifty years is enough / Maybe a bit more). It's a song about knowing you've found your person and asking them to stay forever in the most humble way possible.