Not at all
Attraction to pregnant women is perfectly natural.
A pregnant woman is showing that she is fertile.
As you went through that relationship, you experienced what only fathers usually get to. The beauty, hormones, and that "glow" can be intoxicating.
I have had an extreme attraction to pregnant women since my ex was pregnant with my son.
Unfortunately, it is somewhat unrealistic.
Unless you have a woman ready to shell out babies for you, most pregnant women are, of course, taken.
It may not be a "healthy" pursuit, but not abnormal.