Sigh.. am I overreacting??

My Fiancé has a new friend at work and she’s nice. I’ve noticed though from the minute he wakes up until he falls asleep that they are messaging each other. In the past this has happened & the situation didn’t turn out well like him calling the girl cute who was just a “friend” and it made me upset. I told him i’m noticing he’s talking to her a lot and not to fuck up because I will leave. He promised me everything is good but my intuition isn’t feelin good about this.

It’s killing me what they talk about so I read their messages. He tells her how much he loves me and stuff but he was helping her find a halloween costume because he invited her to our Halloween party and said “not gonna lie this outfit is tight and I’ll try not to be a creep and look at your body in it”

She went out of town this weekend and even shared her location with him???

I’m just confused on how to feel about all this because I want him to have friends but I’m not sure I can trust this girl.