First of all stop expecting her to stop vikrant what he is doing, vikrant and bela were so close befor behir marriage. They were going to accept each other in every way that night, they had spend childhood together. .
Though mahir is able to clear bela feelings for vikrant but still she spend her whole childhood with vikrant. Their is an emotional bond between them and bela is still holding that bond even after loving mahir.
Bela as a mahir wife or lover can be wrong but bela as a vikrant childhood friend is not wrong.
You will say why she never object vikrant touch.
Because she know she don't love him but he still love her. He will take time to accept that he can't touch her and it's true if vikrant was positive also it will take time to accept the fact that she is no more his ruhi..
Secondly bela trust vikrant and vish, if you accept or not. Their every words mean everything to her ( maybe more then mahir) and till bela didn't get any major proof against vish and vikrant. she will never going to suspect them.
Secondly love and trust is two different things. We can love someone but trust it take time to build. For bela nothing is clear and everything is confusion, her mom is shouting you can't trust anyone that means she will take time to trust someone even mahir. On the other side vish and vikrant they have been from 100 year with her. She trusted them and she can't just doubt them..