Part of their friendship is probably proximity and a lack of other AI friends. With Dale and Marigold dating, they probably see each other fairly often. And also going to the same support group. But other than that... May doesn't have many friends in the first place, and Momo doesn't have many AI friends that we've seen. Pintsize really irritates her it seems, and Winslow for a lack of a better term seems to be of a more primitive generator of AI, or so he seems. I doubt Momo feels much in common with either of them. May on the other hand seems broadly similar so I don't see it all that uncommon that they would gravitate together when a group of them are around. I'm going to guess contact is more often initiated by May since again, she doesn't exactly have a lot of friends, and Momo is just that sweet spot of someone she can annoy a lot, but is to polite to tell May to buzz off and leave. So yeah.. I'm definitely feeling the 'sisters' vibe from the two of them.
Something that occurs to me after last week... I do rather hope that Corpse Witch is on the up and up, or when the inevitable blow up happens between her and Bubbles and/or Faye it doesn't involve removing the fight club from the story. Or that it becomes the driving force for Faye and Bubbles to go into repair service together. It was a round about way of getting the job, but I think this is just what Faye needed. She loves working with her hand and metal. But she hates doing dull, repetitive work. And she really seems to be interested in the mechanics of robot and AnthroPC maintenance. And finally, she still gets to engage in the endless snark she enjoys. Clearly this job is much better for her than the coffee shop and she seems genuinely happier with her life because of it.