Should I let go? Or stay?

[LovePink*]

It's easier said than done. Me and my bf been together for over a year. Our relationship has alot of establishments and we always talk about our future and trying to manage the present. Long story short, this friend of his who I don't know, but have an idea of, use to like him. They've known each other for 4 years. Somehow she's came back around because it's his last semester and they have a class together. Every since then, it's like on and off I've been getting gut feelings that ends up coming out of the closet mentally. We're always together so I know it's nothing physical, but I caught her calling him "Babe" in his Twitter DM. Everything else is long story. I'm just to the point where I'm starting to feel the need of letting him go but we've established ALOT together. He doesn't know that I'm considering this though but I'm fed up.