3 month old baby and cheating

Re

Long story short I just found out my SO was texting girls 3 months after we started dating and flirting with them at the beginning of 2020 (supposedly it didn’t go beyond that). After this, I think he stopped (or wanna think he did). I found out yesterday but I’m not sure what to do. I think it’s not that bad but also feel like that’s not what I deserve and can’t trust him a lot. Now I just keep thinking about this.