ASR has a very traditional upbringing...considering Anjali and Nani...and im damn sure that ASR only had La as a means to fend off any marriage proposals...he knows what kind of girl he wants and La is not it...so he has no risk of falling in love with La.
Imagine if he had KKG as his "gf"...two days and he'd be GONEEE...he would fall for her hook line and sinker...hence, no emotional or physical attachment...just an excuse to remain "Unavailable" to other potential prospects...
ASR was with La because he got fringe benefits with La which he would never get from Khushi. We've seen La in his bedroom sitting on his bed so many times. I think the CVs established physical intimacy between these 2 very well. It was never in doubt. Also there is that saying that if you can get the milk for free why buy the cow? No offense to any women anywhere I am one of you :) Just kidding.
If he was with La only to fend of marriage then he sorely failed because La herself wanted to get married towards the end. Yet he didn't. If La wasn't the kind of girl he wanted then he was totally misleading her because she was in love with him yet he was going through this act I guess because he didn't love her. He misled and lied to La. And that's pretty low.
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