Is it normal to always think your boyfriend is going to cheat on you?
So I have this serious jealousy problem (I think) because whenever my boyfriend is anywhere without me (work, home with our roommate who is my best friend, taking my car to run errands) I just feel like there's always going to be some girl whose prettier than me who is dead set on getting my boyfriend into bed, whether she knows he's been with me for 3 years or not. I really hate that I think this all the time, and my therapist once told me I have some kind of hyper-vigilance (something like that) where I constantly think that someone is following me, or something is going to happen to me, etc. I am extremely pessimistic and I've explained to multiple people that I enjoy it, because I'd rather expect the worst and have something better than the worst occur, than expect the best and have it be really shitty.
I've even had these dreams where he ends up cheating on me with some random girl, or even my best friend who is also our roommate, and I think it's just messed up for me to think like this. The dreams are just so detailed and I always wake up from them with my hands clenched into fists.
Am I a horrible girlfriend for my constant paranoia? Is it normal to worry about things like that even though I know he would never cheat on me?