Husband talking to another girl

So my husband and I just moved out of our old apartment and before we left, he gave his number to our old neighbor. I don’t even know this girl, but he’s been to her apartment, helped her put furniture together and did other things to help her out when I’m not around. Maybe I’m just being a jealous b****. They’ve been texting for a couple days now. Should I be concerned? I trust him but I don’t trust this girl because I don’t even know her. What should I say without sounding crazy?