Dear LIB readers: I think my girlfriend is sleeping with my best friend

From a male LIB reader

I can't believe am about to tell you this. You see, I'm the type of person who doesn't believe people should make their private lives public but keeping this to myself is eating me up that's why am sending you this so maybe I could get some advice. I'll go straight to the point. Some weeks back I went to my girlfriends apartment like I normally do. We made out after which she went to take a shower while I was still in bed..she then asked me to get her something from her wardrobe. When I opened the wardrobe looking for what she asked me to get her I came across an Armani case with an Emporio Armani watch (gold plated with black design) inside.
Looked quite expensive. Now at this point I was excited cus I believed it was definitely a gift for me, but it wasn't my birthday and vals was way past, so what was the reason for the gift?.. I decide not to ask her cus I felt she wanted to surprise me and I didn't want to ruin it, so I kept quiet about it, waiting for the day she'll present the gift.. 

Couple a days passed and nothing, no gift from her and I felt maybe she was waiting for the right time.. What happened some days later was something I can't put in words. My best friend called me up for drinks so I met him at our usual beer parlour. Now at first I didn't notice but for some reason I glanced at his wrist and to my surprise he was wearing the same wrist watch I saw at my girlfriend's place..I told myself it had to be a coincidence, maybe he bought the exact type ,i mean what other explanation can there be? That my bestfriend is wearing the exact type of wrist watch I saw at my girlfriends place? Maybe am just imagining things. I don't know anymore that's why am writing you this hoping maybe someone out there can help make sense out of this cus I refuse to believe that my bestfriend of many years, someone that's practically blood is screwing my girlfriend..