Is it possible to tell if a partner is lying?

I’ve been seeing a guy for several months now, and it’s at the stage where I’m wondering whether to become exclusive or ‘break up’

He’s a nice guy, but he constantly plays ‘pranks’ on me by joking about something in a completely serious manner, and then once I fall for it, he’ll tell me he’s just joking. For instance he told me a completely believable story about how he was homeschooled, and when I asked him if he ever wished he went to a school with other kids he burst out laughing and said he was only joking.

I know these pranks are relatively minor, but because he’s so good at keeping a straight face I can’t tell whether he’s telling the truth or not unless he tells me (and I choose to believe him). I’ve asked him to stop but he says it’s cute that I’m so gullible 🙄

I feel like entering a long term relationship with this man would be a bad idea, because if he lies about big things (like cheating, etc) I wouldn’t be able to tell.

I’m just wondering if there’s any correlation between pranks and lying? My biggest fear is getting cheated on in a relationship so I’m wondering if my opinion is just biased?