Is he cheating

Hello background story. I have been with my partner for 3 years now and have a baby together.

We split for a few weeks in 2019, whilst we split he spoke to someone and they got on well which I’m so glad they did because he needed support.

Anyway I left him when I was pregnant and towards the end of my pregnancy he said he wouldn’t be at the birth as he wanted to be at this girls birth (was a month a head of me)

I found that in itself booky but moved on from that.

I found out a couple months ago he messaged her saying he was gonna take my daughter away to live with this girl so they could raise her. His been saying I love you yet he claims his never met her 😂😂. I was informed they had sex in October but he claimed he never met her. Does anyone else have suspicions of this girl. I have asked him and her to block each other as it’s making me feel uncomfortable. I got loads of abuse off the girl and my partner had the hump with me. I feel like he might actually have feelings for this girl. Sorry if this is all over the place just sat here crying as I just see on social media his been calling her gorgeous and I really don’t know what to think anymore. 😩😢