Am i wrong for being upset that my boyfriend asked for a threesome?

It all started yesterday, the conversations we had just threw me off. It started with the morning questions he asked .. the first was “do u actually like the sex we have?” and second was “what’s an open relationship” he claims he really didn’t know what it was and that he thought it meant u can ask ur partner anything. So whatever i let it slide, then I asked him what does he want for his bday & he responds “threesome” but then tells me he’s joking. But we have never joked like that before.