sims that are married or in a relationship

I had one sim that I sent on a couple of dates each with the 3 cutest townies in town, LOL. She got equal time with each of them and a roughly equal amount of interaction commands from me. There was one guy she had absolutely no chemistry with even though they got along and spent quality time together. Another guy was the clear winner with the most pink in their relationship bar, so that one became her boyfriend. I've noticed that my sims' friendship and romance bars will fill up at different rates with different sims, so I think it helps to set them up with someone they have a natural attraction to in the first place.

Usually in my case once they have a kid they rarely do flirty interaction autonomously

My sim couple have 5 kids but they still act like they are on their honeymoon. I play with full autonomy on but help them retain both friendship and romance at full. They never stop talking to each other and do autonomous romance all the time. They follow each other e.g.. If I send one to garden the other will autonomously come and help. They kiss a lot and they have trouble containing their excitement when one comes home from work. She dated several guys and he was her clear favourite so I married them.