Hi Archana,
Your boyfriend may be very attentive when it comes to this other girl because he may be getting bored with his two year relationship with you.
He may have taken his relationship with you for granted and thereby feels a lack of excitement in it.
He may feel a sense of renewed excitement whenever he sees this other girl in the classroom or she is being talked about by other classmates.
He may find her to be attractive and wants to learn more about her.
In his mind though, he may not really believe that he is doing anything wrong. This may be why he has been talking about this girl to his friends quite openly for a year.
He may think that as long as all he does is talk about her, he isn’t cheating on you.
Being that he hardly knows this girl, it is unlikely that he has reached a point where he has developed truly deep feelings for her that could feel like love.
However, the more he remains curious about her, the higher the likelihood that he may try talking to her at some point and this could lead to even deeper feelings.
Try to talk to your boyfriend about how he feels about his relationship with you and what he thinks the both of you can do to make your relationship even better.
There may be something that is missing in your relationship with him that he may feel that he could possibly get from this other girl.
Perhaps the both of you are just not trying to discover more about each other anymore. Perhaps the activities that you both engage in are always the same and have now gotten boring. Perhaps you both tend to be isolated when you are together and rarely allow new people into your lives.
The sooner the both of you figure out what is deficient in your relationship, the sooner you will both be able to fix it. Upon fixing it, he may not feel the need to keep looking at or talking about this girl anymore.