Here's a theory that I've put together from the whole of this arc so far. I think that May
did remember who Sven was and Momo's reaction to him. However,
May herself found Sven attractive, not physically but rather because of his witty banter. So, I'm going to posit that she looked for reasons for believing that she wasn't 'poaching' from Momo. So, it was a case of: "No, this can't be the guy Momo's crushing on because he doesn't have a man-bun! So, let's do this!" Panel 5 is May just realising what a thin layer of justification and sophistry this was.
Ultimately, this will go into May's list of: "How my lack of impulse control has and continues to screw up my life." At that point, she'll also recognise that she actually
likes Clownboy and things may go forwards from there.
Yup, not unexpected. It does raise issues on how android memories work... she literally didn't recognize Sven without bun? Or is May just a bit ditzy?
As I say, I've got a feeling that May at least suspected that Sven was the same person that Momo was crushing on. However,
she wanted him now and so told herself that it
couldn't be the same guy. Well May, congratulations on joining the human race with our tendency to tie objective reality into knots so it matches our desires and beliefs.
Finally, yes, people
do change hairstyles. For example, I've suddenly realised that Momo is wearing her hair in a Weiss Schnee-style sideways ponytail.