My cats have fallen out :(

[DanHumphreyIsA]

My two cats seem to have fallen out, or rather BoyCat has fallen out with GirlCat.
They came to us at differenct times, Boy second, and they have up to a week ago been best buds. They loved chasing each other around, jumping on each others heads and grooming.
In the past week Boy has started growling and angry-meowing at Girl every time she tries to play with him. He doesn't react if she's just there, only when she's tapping him on the head, or hopping up to him to start playing. Even if she tries to groom him, he moves away.

I feel so sorry for her as she's very timid and doesn't like too much human contact, she'll happily sit near us and sleep next to us but if stroked or approached she runs off and hides (normally behind things like glass doors) she's not really interested in any toys etc, only likes to play with him.

There is an outdoor cat who has started coming to NDNs garden and recently ours has been hiding out in our garden more when he's there, so I wonder if he's maybe had a scrap and now doesn't like any other cats? Is this possible, will it pass?

He is otherwise acting normally with us, isn't showing any signs of being hurt, no other behaviour changes.

I have tried to play with her a bit, otherwise she won't move all day apart from to eat/go to toilet but she's not that interested.

How do I tell a cat to make friends and play nice?!

The same happened to my cats! Unfortunately they still don't like each other.
They adored each other until they started going outside ( 5 ish years ago) and I'm guessing that encountering other cats made them turn on each other.

Oh dear .. the girl is indoors due to health problems, but the boy has always been outdoors as he was a stray so used it so we have to let him out. Up to now its not been an issue.. Can yours still be near each other or do they just react when one tries to play with the other?

Mine can still tolerate each other the rest of the time, and still sniff each others bums lol! It just kicks off when she tries to wrestle.

Is he feeling ok? Mine gets grumpy at his friend whenever something is wrong, e.g. a stuck hairball will make him hiss at her and grab her when he usually dotes. It's actually the easiest way for me to tell something is bothering him because he's rubbish at giving any clues otherwise.

He seems to be, it's never happened before so I don't know if it could be a sign of something else. He has been eating a bit more geass outside and has thrown it up a couple of times (first time I've ever seen him
throw up was a couple of weeks ago, all grass) so maybe thats stressed him out too. The only other time he's been poorly was when he hurt his paw, but we didn't notice a change in his behaviour apart from a limp.
I hope they make friends soon, the girl keeps trying to entice him to play but none of the usual tricks are working

It sounds like the interloper cat in the garden has upset him, yes. This could be making him more stressed and reactive to your girl cat. It's not necessarily that he hates her, he's just stressed. I would be making moves to 'discourage' the other cat from being in your garden and also try a Feliway diffuser in your house.

Mine tolerate each other to a degree. 90% of the time they live side by side and ignore each other. Occasionally they will hiss at each other and one will try to start a fight. They never actually fight as one always runs off. If they see each other through the closed patio doors they will go mental jumping at each other, hissing and growling.
Having said that they eat from side by side bowls, share litter trays and sleep in the same room each night. They never groom each other or sleep curled up together anymore though.