Advice please read.

I literally get the exact same thing! I have thoughts of over people randomly pop up in my mind and then my mind tries to say that because the popped up then that must mean that I like them... But to make it worse, I also feel the requirement/urge to tell my spouse... Otherwise I feel as if I am lying or keeping secrets... All this to say, you are not alone, and your post helped me to not feel alone too.

I've been through a similar thing and me and my partner have tried individual researching on our own how to deal with each other's "big feelings" (my ocd and his adhd) as we call them. Learning specifically how we can be better partners to each other despite having these feelings cause they aren't going away soon. I think communication is best but explain to him if you haven't yet how others have felt this way to and showing him so he knows more that it's not somthing you want to be thinking.

With compulsive honest and feeling that guilt I wouldn't bring up to him specifically his brother because thats not what actually seems like is the issue it's more the thoughts that came on your own. Explain that you are still having a hard time forgiving your self for certain thoughts and letting that guilt fill you when you haven't done anything wrong but its the brain telling us we have. Maybe go about it with him that you would really like his support in talking through when your feeling that guilt or compulsion of past people, without details of who and more why you can't feel ready yet to move on from that memory

Ive had it personally with my husband that I felt guilty for thinking about my ex and wating to contact him, not because I liked him still or cared about him but because i was needing validation from a controled person sinceI felt like I have been losing control of myself. With my ocd the more I feel im losing control of everything the harder it is for me to accept things changing and want to go back to what things were. It took alot of talking but my husband understood a little more each time I talk with him, not on how to fix the issue but how to help me navigate my feelings about the compulsion and how he can understand why I'm feeling it. There's normally always triggers to the compulsion and figuring thoes out helps to avoid it happening more and more!! Hope this helped a little :)