Bit hard to model healthy relationships when you're single yourself.
I'm very conscious that dd has perhaps gone too far the other way!
Her dad and I split up when she was too young to remember us together, I've unfortunately not met anyone since who's made it past the 6 month mark, for various reasons so she's grown up with me being single and not seen what I'm like in a relationship.
She is 18 now and holds her boyfriends to VERY high standards but I've noticed recently perhaps too high.
She can be very black and white, is honest to a fault herself and expects the same from others (including platonic friends - fortunately her bff is the same) but she can be unforgiving and a bit tunnel vision.
I don't think it helps that she knows why her dad and I split, I didn't go out of my way to tell her this but eventually she reached an age where she started asking questions which was around the same time as she was learning about human reproduction and her dad and I were always honest about when we split and she knows her half siblings dob so... She put 2 and 2 together.
She was mad at me for "covering" for ex which I don't feel I did I just didn't want to burden a little girl with that stress.
What also didn't help is that when she asked her dad about it he handled it REALLY badly! Initially trying to deny, then blame me, then the "stress" of becoming a father so essentially blaming HER... 
That was a nightmare to deal with when she came back from that particular visit.
Then he and wife 2 have a shit relationship and she actually caught her dad kissing someone else at
one point too! Fuckwit!
So what would people suggest single parents do as far as "modelling a healthy relationship" goes?
Plus not all single parents want another relationship for various reasons.
I know someone who was widowed, her husband really was the love of her life and a truly excellent husband
and father. He really was a gentleman. She had/has no interest in dating anyone else.