We're not dating, just talking. but he keeps bringing up about "making you my wife one day" and he calls me beautiful every time we talk!
If a guy keeps joking about making you his wife, does that mean he's serious about you?

He has at least thought about it. The reason he makes it sound as though it's a joke is in case the comment makes you upset. If that's the case then he can simply say, "Hey, I was only joking."
Id say he's joking at this point, because you're not even dating.
Yes, he definitely plans to keep you around and most likely really has considered marrying you.
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Next time he says it. Open Expedia and show him you could be in Vegas and married in a couple hours.
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