Casual friend keeps asking me for threesomes?

Chileè

So I was seeing this guy briefly for a couple of months. We had a fight, made up and reconnected like a month later. But recently I’ve realised that our sex just isn’t what it used to be so I’ve been distancing myself and he just keeps asking me for threesomes. I did one with him which wasn’t really an issue for me but why won’t he just someone else. His got a lot of options and it’s starting to get on my nerves to the point that I am gonna lash out at him again. Thoughts?