most probably he looked a little guilty when paro mentioned about not being able to keep her fast because he has forbidden it, but if rudra goes about fasting then it is hypocritical of him. this is cliche every hindi serial does this if heroine doesn't eat good hero can't eat either. but the point is recycling old ideas is ok but if they give it a special rudra and paro flavour to them then the scene becomes their own and with such fine actors they will put their own signature on it.
i predict something like paro faints in shock and rudra runs after the bad guy but he doesn't get too far. lights come on and paro health calls him back to her side. doctor is called and maithili fesses up that paro didn't eat anything either. rudra loses it and yells at everyone to leave as no one is capable of looking after paro. when she wakes up she is shivering upset he calms her down but paro is still too distraught and cries that someone is going to take her away from him and she is scared. rudra confesses that will never happen because he has kept fast/mannat for her, if her prayers can be heard by bolenaath then why not his. this calms paro down as rudra will never let her be lost and they break their teej fast together after a unified wish of always being there for each other.