A relationship without trust becomes an investigation with feelings attached.

Without trust, a relationship turns into surveillance with affection attached. You start checking, interpreting, and building cases, and the other person starts explaining and pre-empting, and both of you spend enormous energy on something that used to be automatic. It is exhausting in a way that is difficult to sustain for long. The affection can be entirely genuine and it will not carry the weight.

If you recognise this, notice how much of your day goes to monitoring. That is the actual cost. Then decide whether trust is being rebuilt through changed behaviour or whether you are simply managing its absence indefinitely.