I don't want to offend anyone here but I would like to express my thoughts.
I fortunately or unfortunately do not believe in love at first sight.
I feel that when you first meet someone you can be attracted to them, you can be drawn to them or mesmerized by their presence - but LOVE - that doesn't happen just by looking at someone - IMO.
I feel that in order to love someone you need time - to understand them, to feel what type of a person they are, what is in their heart etc - just by looking at someone or a few chance meetings - that doesn't happen.
But I will say this - pop culture, hindi movies, over glorified romance etc have skewed the meaning of "love" to a point where people use the term so frequently and freely its lost its depth. Its so easy to say "i love you" "i love how you make me feel" etc but for one to REALLY prove their love or maintain the responsibilities that come with that are few and far between.
To quote deepika's line as Naina in YJHD - people say I love you but then those 2 people can't handle/maintain those 3 words.
So in that sense I don't find SidNi realistic but I do find them to be the epitome of bollywood logic - boy girl meet once or in this case a few times and boy falls head over heels in love upon first meeting and day dreams about her constantly.