Mysterious is choosing what to share. Secretive is hiding what you should share. Know the difference.

Both look like withholding from outside, but the direction is opposite. Choosing what to share protects something that is genuinely yours and harms nobody. Hiding keeps back something the other person needed in order to make their own decision, which moves the cost onto them. The test is whether your silence is protecting you or costing somebody else.

Look at something you are not saying and ask who carries the risk of not knowing. If it is only you, keep it. If it lands on them, say it soon, because that kind of silence grows faster than the awkwardness of ending it.