I don’t know if this is ducktales or not, but there are very few women that are content with sharing a man.
If she is content it’s usually because she has something on the side herself, she’s using you until she thinks she has a better option, or you’re the best she can do in her mind.
If this is true I’d even be skeptical of her pregnancy, she might be carrying some other man’s kid and feeling guilty so she’s letting you have some freedom for a little while.
It’s generally always deeper than surface level with women.