I agree with leo 100%. You have to accept that you cannot control or suppress these thoughts. Im 33 now and have had anxiety since childhood. I experienced some intrusive thoughts in my 20s but never to the extreme that I have the past 10 months. IT has been a nightmare and any progress that I had previously made with my anxiety/ocd is now gone. My thoughts are violent, sometimes sexual but not often, fear of losing control or impulse control, contamination etc.
I wonder if maybe you have some insecurities about yourself that may deep down make you a tad jealous? Or if its just purely an intrusive thought? I can understand the thoughts you are having b/c I could see myself thinking the same stuff.
I am somewhat jealous in my relationships. I do not know how to trust people. I have been married for about 9 years now and even to this day if my wife calls and says, "im gonna be running a few minutes late coming home from work" my mind automatically starts throwing thoughts at me that she is seeing someone else. I have no reason not to trust her. It makes you sick to think the thoughts but you have no control over them. I also notice that when I have been to her work to take her something if theres a new male worker I start having thoughts about him trying to hit on my wife or them sneaking around behind my back.
So, I can definitely relate to how you feel. Im sorry I dont have any answers for you but just wanted to let you know that I share similar thoughts and that you arent alone.
I can tell you this. If someone does ever hit on her and she tells you about it. Do not let her see how angry it makes you. She may never tell you again if it does because she doesnt want to see you get into trouble.
There was a delivery man that had been hitting on my wife at her work and she had confronted the man and he still didnt stop. The store manager would actually always be around my wife when this guy came to deliver because it he made her feel uncomfortable. I personally blame the company she works for, for not having called the company he worked for and let them know of the situation. A few weeks later he caught her taking a break with a female co-worker. He walks by her playing with his phone, turns and looks at her and says, " I'd give you my number but I bet yer husband wouldnt like that would he?" she replied "No he wouldnt and he's not gonna like when I tell him when I get home!" She had no idea I would lose it. When she told me I was sooooo mad. I called a friend and found out who the guy was and I caught him out in the parking lot of a grocery store. I have never seen a grown man so scared in all my life. After meeting me he never delivered to my wifes store. He actually had his route changed and then later found a different job altogether. My wife was pretty upset that I went after this guy for fear I could have went to jail or she could lose her job. I tried to assure her that if they fired her I would sue the company as they had several complaints and should have done more. If I could do it all again. I wouldnt change a thing. Sometimes you got to put a man in his place.
Back to the topic.
Try and just let the thoughts come. Practice not reacting to them with that sick in the gut feeling that you are getting. I know you know what Im talking about. Let the thought come and just tell yourself. "That's irrational, my girl loves me. If she didnt she wouldnt be with me." The guy is her EX for a reason. I hope you get some relief from this soon my friend.