Well, it's good that you say that. Unfortunately, I've seen it done in subtle ways and at the same time, the parent doing it denies they are disrespecting the other parent. It's usually the mother who undermines the relationship with the father. Maybe because mothers usually get custody. Maybe for other reasons.I am never going to trash talk my husband to our daughter.
Just think. You don't like your ex (or soon to be ex), which is why you are leaving him. You think the OM is great, which is why you are going with him. Try as you might, some of that attitude will go through to your child. Kids absorb that sort of thing by osmosis.
And you will try to encourage a relationship with your new husband (OM) and your child. We see all too often that the new man becomes the primary father figure and the child's real father becomes second tier. I think custodial mothers sometimes underestimate how much of a role they played in that happening.
It takes an extraordinary effort to encourage your child to keep their primary father relationship with the man you left for someone else. You left him because you felt the new guy was better, and some of that attitude has to show through to the child.
Family counseling may be helpful for the future.