I’m 28 and my partner is 24 we haven’t been together very long but we were friends for years before , things are pretty serious he’s close with my son. Told eachother we love eachother etc and spend a lot of time together. He was on a night out with his friends last night and I’ve noticed whilst he was out he has started following an 18 year old girl on Instagram(no mutual friends) , my gut is telling me it’s somebody he has met her last night and that’s why he added her. Is this a red flag or am I being over sensitive ?