I caught my boyfriend talking to another girl

Hi guys for context i’m a 19f and my boyfriend turns 21 in. a few days. We have been together almost a year. I usually don’t ever go through his phone but this morning i had a really weird feeling and decided to look through it and i found in his recently deleted messages him talking to another girl. He initiated the conversation and was calling her pretty, saying he remembers her beautiful eyes, that he hopes she had a good day calling her love and all that. He never talks to me like that. I confronted him and he lied at first and said it was his cousin, and i said there’s no way you talk to your cousins like that. Then he switched up and said it was one of his old friends, and then finally came clean and said it was just a dumb mistake he didn’t know what he was doing blah blah blah. He says he didn’t act on anything which i know is true because he lives at my house and doesn’t go anywhere since he got laid off a few weeks ago and i have his location. He already blocked her and has been apologizing non stop. We had a huge argument and i don’t know what to do. I’ve caught him in multiple BIG lies since we have been together. Should i dump him or try and work things out? He was there for me when my father passed 3 months ago and I don’t want to let him go, but i feel like i should. 😞