Its sounds like you have your NRAAS Story Progression mod on the default speed setting. So the romances, babies and other progressions happen each "sim cycle" which on the default setting is quite often. The same thing that's happening to you happened to me, and while my sim was trying to get on with her career and improve her house, everyone got married or whatever and then the only single sim left ended up being the male maid, and even then he had a bunch of lovers, so after they got married I made him go around and break up with all of them ..
So now, in a new game I always pause my game and then go into Story Progression, and if I can't be bothered going through all of the little detailed settings, then I at least set the main one to "snail" speed. To do that, you click on a computer in the game, like at the community library or on your own sim's computer, and click on NRAAS ... Story Progression. Play around with it, you'll eventually find the setting I'm talking about. If its not slow enough for you, then go through the detailed settings, and in the Flirt and Romance sections, set the speed to something like ... 5000, cool off between firts, partners, breakups, a longer amount of days, something like 50 days, and you could set the bar higher, the "liking gate". I also do that for stopping them from moving around and for stopping so many townies getting generated and taking up all of the empty houses, and preventing the iconic pre-mades from breaking up, or at least so easily. At the NRAAS website, there is a page that has an explanation for what each of the little settings is for, but I think most of them can be guessed.
And those settings don't have to stay that way, once you're ready for things to populate and progress here and there in this facet of life and that, go back in and change the settings to how you think would do the trick.
This is a reason why I get my sims to take a laptop in their inventory to the vacation worlds, so they can set the things for that at a desk somewhere. And they do so on any of the computers at University as soon as they get there for that world.
If I go into my game on an occasion when it says "it appears the age span has changed would you like to change the story progression speed settings ... " I click "no", because I've usually gone to a lot of trouble fine-tuning the detailed speed settings how I want them.
Maybe there's a tutorial video of it somewhere.
Be a hundred and swim in sims .