Floridagal10 wrote some fantastic strategies. I'll try to add my own advice in hopes that it can only help more.
It's difficult for me to give any advice specific to your situation since I'm not sure of your history with your boyfriend or your anxiety in general, but I can still relate to you in some ways.
A little background on me: I'm 24 and have been seeing therapists on and off for the last 12 years. My symptoms fall into the categories of General Anxiety Disorder, Panic disorder, and OCD, but in the end I just like to say that I think too much.
I experience these "negative movies" like you do, but they are usually about something different. I am extremely anxious about friends and family getting hurt in any way, and sometimes I can't help but imagine terrible scenarios in my head where things happen to them. I don't want to think about these things, and I know logically that they aren't happening, but for whatever reason I can't help obsessing over them.
Perhaps more similar to what you're describing, I also have negative thoughts about what friends or even strangers are saying about me or things I like. For example, a friend of mine might make an off-hand negative remark about a shirt someone is wearing. From that day on, I might randomly think of that remark while I'm dressing myself in the morning. I'll think things like, "he probably thinks this shirt looks dumb" or "I bet he thinks my style is stupid", etc. Sometimes I get angry about things that he never even said! It's all stuff that I imagine
him saying. Logically I know he isn't saying those things, but somewhere deep down I almost believe that he is.
The commonality between people like us is that our minds are grossly over-active. Our imaginations have grown so strong that they seem to stomp on any logic we throw at them. We are our own worst enemies. That is both the worst and best part about anxiety. We are capable of putting ourselves in the worst moods imaginable, but we can destroy what we have created with practice.
These thoughts and just negativity are making me feel like I'm going crazy because I can't stop them from creeping up.
My first piece of advice is to take a step back and understand that this is beatable
. I know this sounds tired and overdone, but it's absolutely necessary to understand. Too many people with anxiety approach it with a doom-and-gloom mindset. "This is going to be my life forever", "my mind is messed up", "I'm going crazy", "I'm going to lose my friends", blah blah blah blah. With that approach, you set yourself up for more anxiety. Again I stress, we are our own worst enemies. You are not sick, you are not messed up, you are not broken beyond repair.
As for how to stop these "negative movies" before they start, the answer is in the question. Literally, you STOP thinking these thoughts when you feel them starting. This is something that will take practice and a lot of time, but after a while you will probably notice that it will be easier and easier to not think these bad things. You have to resist the urge. Chances are, you don't WANT to think about your boyfriend cheating on you, but you have this uncontrollable feeling that you HAVE to. It's as if by not thinking about him cheating on you, something bad will happen. If you feel any inkling of those thoughts approaching, you feel obligated to indulge in them.
What you need to learn to overcome is that feeling of obligation. Think about what has come from these negative thoughts. Have they fixed anything? Did you successfully catch your boyfriend cheating because of all the negative thinking you've been doing? Have they helped in any way? Try to remind yourself about what you wrote in your post:
It has come to the point of affecting my relationship and my boyfriend couldn't take my accusations and negative thinking.
Clearly, judging by your post, they have not helped. They have only created tension within the relationship. THIS should be your ammo for dealing with the thoughts as they start to creep up. Fight the urge that you HAVE to think about them with logic. Think, "these thoughts have only hurt me and my relationship and have done nothing good. I do not have to think about them."
Like Floridagal10 mentioned, distraction can be a great tactic. Try to use distraction in combination with what I just mentioned. When you feel the thoughts approaching, remind yourself of their worthlessness, then immediately find a distraction. Change the channel in your head. Play a game of cards, watch some TV, cut your nails, clean your room, flip through old pictures of fond memories that make you laugh, go to the super market, do some exercise, anything! Don't try to "fight" those thoughts, don't give them the time of day.
Remember, you've already started the healing process by admitting that you need help. That is one of the hardest parts about beating anxiety, and the best thing you can do. From someone who has been going to therapists for 12 years, I cannot recommend it enough. Talking to another living, breathing person relieves tension. People are often skeptical about therapy because they think that the therapist will just say some generic bullshit, take your money, and send you out the door. But let me tell you, sometimes I feel the best after a therapy session where the therapist barely said anything at all
. You know those feelings of, "I'm gong crazy", "I'm broken beyond repair", etc? Those are what therapy helps with. You can say your deepest, darkest thoughts that terrify you, and they will nonchalantly converse with you as if you're talking about the weather. It's not that they don't care, it's because they've heard it all before. That alone can calm you down. You are not alone in your thoughts. You are not un-salvageable. You are a lot more normal than you think
I hope this helps in some way or another. Again, I'm going off of only what you wrote in your post, so I had to make a lot of assumptions. Please don't hesitate to discuss this topic further.
Keep your head up.