i mean, it is 'ew' given that "serial killer girlfriends!!!" sounds more like "omg fred and rosemary west are goals <3" than "oh wow they'd make great girlfriends and i ship them", which would be a more healthy and appropriate way to approach shipping.
having said that, the response is definitely homophobic. it's not about the worrying part of the comment, just the mere mention of lesbians. ...which is creepy on their end. lesbians > murder