I’m doing rotational play these days and disabled long term relationship for inactive sims. But I enabled their romantic interactions so I wanted them to have romantic feelings to each other but control their relationships when I actually play them. But what’s happening is single sims are becoming very promiscuous. In their memories, they change their woohoo partner so often and their memories section is full of ”woohoo with” and “caught ...cheating” . Even sims without commitment issue trait are like that too...I feel like the system makes them moving on to another sim because I disabled them to have a long term relationship.

Will there be any solution to make it more realistic?

I'm not sure if this is what you're looking for, but I disliked that happening in my inactives as well, and wanted more monogamous couples. My solution was to limit the number of romances a sim could have to one. I believe it was under a SP romance setting, but I don't know if that works with long term relationships disabled.
But I may not have done that in my current town as recently I had a formerly active married couple where the wife began 'dating' another townie after the birth of their first child! Apparently it was only a post partum fling as I received messages soon after that she was dating her husband!
I should probably go check that setting again.

Is there a option for controlling the number of romantic interests under a romance setting? Could you please tell me whats it called?? I can’t find it..

Okay, I finally found it! It was actually under flirts rather than romance and I hadn't limited in my current town either.

On city hall or any computer: NRaas > SP > General Options > Options: Flirt > max allowed per Sim

The default is 0, which is unlimited, so pick a number you're comfortable with.

I hope this helps in your game!

Thanks Deedee!!! You are awesome!