Blue tit nest box

Hi I'm new to this great site

I watched the blue tit build her nest in my box in March  activity slowed down after thought might be laying  her eggs not seen either for over 3 wks now the male is bk around not seen her tho

Thought they must of abandoned the nest for a reason unknown to me accepted this only to see some starlings trying to get into the box in the last 2 days but no sign of her could she be still be sitting  or has she abandoned it??