Being friendly with everyone and trusting everyone are two different settings. Keep them separate.

Warmth and trust are two separate dials and most people wire them together. You can be genuinely pleasant to everybody at your school or your job, remember names, ask about weekends, and still keep the serious information inside a very small circle. Nothing about that is fake; it is just accurate. The mistake is assuming that being nice to somebody obliges you to tell them things.

Practise holding both at once this week. Be friendlier than usual to people you do not know well, and say nothing you would mind being repeated. Then notice how much easier it is than choosing between the two.