Either way, it's an issue, but it matters more if he's lying about important things. If it's just stupid things, does he lie to other people a lot? He may just have trouble telling the truth. But as long as he trusts you on the important things, you probably don't need to worry.

If he can't tell you the truth about stuff that matters, though, you should have a serious convo with him. If he won't do that, threaten to dump him. He needs to realize you're serious.