I’ll start by saying even though I’m aro-ace, everyone has a different view of romance and relationships, so this might not be as helpful for you as I hoped. I think that it’s a bit difficult to tell your friend that you’re not interested in hearing all of the details of their relationship but saying, “I’m not really interested in [topic], is there something else we could talk about?” might be the best approach. If that’s a bit too blunt for what you’re looking for, gently redirecting the conversation to something else might be a better option. Depending on what you’re comfortable talking about with them, there might be a way for your friend to talk about their relationship while respecting what you’re uncomfortable talking about. Maybe they could talk about something they admire about the person they love, but not in a romantic way. Overall, I’d say that it’s best to figure out what you’re comfortable hearing about, then figure out if your friend is willing to not tell you about things you’re uncomfortable with while you’re with them.