I think you've been incredibly foolish. And maybe she's been as well, having a kid so young. But we're talking about you
and your choices
I get that you are a young man and God knows you're not mature yet. And it shows.
If you love her, then you find a way to at least tolerate her kid, who she loves. Period. There are no weasel ways around this.
And since you don't, then guess what? You probably don't love her.
Can you two be friends? If I were her, I would kick your sorry ass to the curb and block your number. I am not kidding. To not support her emotionally, and her child (who by definition is a preschooler, and therefore a ton of work)? I would find that very hard to forgive.
You don't have to change diapers (although it would be nice if you did) and have the kid call you Daddy for you to be supportive. Instead, you threw this up as a barrier between the two of you, one she cannot change or erase.
What would it take to make you a couple again? The death of her child? The erasure of her child from existence? Sending the kid out for adoption because you
aren't comfortable with her?
Yeah, I would tell you to go scratch. And your ex should, too.