Need help

Me and my ex got back together 5 months ago we have a 6 year old together, he wasn’t there for her for 5 years then he got involved a year ago he told me he loved me still and wanted to try again but I said we’ll make this about our child only (mostly to see if he’d actually stick around and wasn’t there just for me) we got together after a while and I’ve just found out while he was telling me he loved me he was texting another girl saying the same things this obviously hurt she had a partner so she wouldn’t go out with him he only stopped talking to her because I said we can take this slow and work things out, I just feel like a second option to him and I don’t know if I should stay with him or leave him because of this he left me for 5 years but spoke to her the whole time telling her he loved her but tells me he loved me the whole time we weren’t together and he wasn’t never interested in anyone else and never was close to another girl (he left while I was pregnant and got with a girl a week after) I’m just so confused he said he didn’t mean what he said to her but he said it everyday and not a day went by that he didn’t talk to her or call her yet he was ignoring me and didn’t come to see me or our child for 3 weeks. Any advice would be great 😩