Is my friend just using me?

Firstly, my husbands cousin 27M is crashing on our sofa, which I’m finding quite stressful on its own. He moved from another country, doesn’t speak English and we’re supporting him while he gets settled. My long time friend 36F has been introduced and now they’re suddenly crazy about each other in the space of about 5 days. My long time friend has been to my house maybe twice in 3 years but came to visit him the day after they met and now wants to come and hang out on Friday. Our communication has gone from sporadic to daily and every conversation is about him, what he said, questions about him. They have nothing in common, including language, she is also dating another guy which I’m not allowed to tell him. The whole situation is annoying me and making me stressed but I can’t pinpoint why it’s bugging me so much. I think it’s just the whole scenario. Now he’s asking to invite her to events that we’re attending with my family, like I can’t escape loves young dream. What can I do to handle this better?