Attractiveness Gone

Oh interesting! I didn't see anything in the patch notes suggesting this should be changed.

What are her turn ons/turn offs?

Has he recently gained a new skill or job or university degree?

Is he currently wearing an outfit she doesn't like?

I changed his outfit before the update. But she was still attracted to him. Maybe go back to the other outfit ? 

If you wanted to test whether it's the new outfit that's the culprit, you could add his old one as an extra outfit and have her interact with him in it. There can be a slight lag with the attraction updating though.

Sims can be more or less attracted to other sims when they're wearing a particular outfit, depending on the clothing style and colour and their turn ons/offs.

I sometimes change the clothes to suit the partner's preferences, but I more often change the turn ons and turn offs to include their hair/colour/clothing style if I already like the sim's look. Or I just go with them falling out of attraction if I'm in the mood for drama

I changed it back & she still isn’t attracted to him 

Ah bummer. I wonder what changed!

Are you using any mods? And you mentioned he hasn't gotten new traits, but does he have any new lifestyles?

As a workaround you can change your sim's turn ons to include more of the boyfriend's traits/hair colour/skills.