Feeling alone

I’ve never felt more alone than ever with my intrusive thoughts. I feel like no one has this one thought in y head and I wanna cry cause what if it’s real and I’m just trying to deny it? Basically my head is obsessing over my boyfriends friend and is making me think of him a lot and making me think that if if my partner leaves me that I should just go with his friend or that I like his friend or that I wanna be with his friend and it makes me imagine things with his friend and it’s getting to me so much I wanna cry I wanna stop thinking of my bfs friend and I want these thoughts to go away I try to make them go away by being calm but then they end up feeling so real I don’t wanna tell my partner about this thought cause he’s then gonna over think and I don’t wanna hurt him at all I jus want these thoughts of his friend to go away. I wanna be with my boyfriend only forever.