Is it a red flag that my husband and I never argue?

It can be either, and only you can tell which. Ask yourself: when something bothers you, do you bring it up and it just goes smoothly — or do you swallow it because it's not worth the friction? The first is a genuinely easy fit. The second is a bill that comes due later, usually as resentment or distance. No conflict isn't the goal; feeling safe enough to have it is.

For what it's worth, some couples really are just low-conflict and it's fine. If you both feel close, heard, and like you can say hard things when they come up, don't go inventing problems. The test isn't how often you fight, it's whether you'd be able to when it mattered.

Not automatically a red flag. Some couples are just genuinely aligned and easygoing, that exists. The question isn't the fight count, it's whether hard things actually get said. Do you tell him when something bothers you, or do you let it go because it feels smaller than the peace you'd disturb? That's the part to check honestly. Try this test: think of the last time he did something that mildly annoyed you. Did you mention it, or did it just evaporate? If you can't remember any small friction ever surfacing, that's worth noticing, not because conflict is good, but because total smoothness for six years is unusual for two separate people with real preferences. Ask him directly, not as an accusation, more like curiosity. 'Do you ever hold stuff back with me?' His answer will tell you more than any theory will.