Islanders always lose a little popularity when they choose to recouple after Casa Amore, moreso the guys than the girls (since most of the Love Island viewership is women who would sympathize with the girl in that situation). Some of them bounce back to their original popularity since viewers change their minds about how they feel towards all the contestants on a daily basis, so I wouldn't be too concerned for Nas.

The fact that Nas was getting a lot of pity for not having anyone interested in his early on was also a big reason for his popularity, but a downside to that popularity is that a lot of people want to see Demi as either Nas' dream girl who he should see as a 10/10 with the perfect personality just because she's the first one that showed interest in him, or they think that every girl who shows interest in Nas (both Demi and now Eva) are just faking it because they know he's a fan favorite and those fans criticise Nas for being gullible enough to fall for it.