Is my husband cheating or pregnancy hormones?

I just wanted a few opinions from you women who have had similar situations & to see what you have done. But basically before me & my husband got married there was this girl in the military he talked to while he and I were engaged. They never dated or had sex but he was texting her behind my back (yes he was interested in her but he says to make me jealous) and i found out. Ever since that he had to show me that he would never do that again. I forgave and we continued on with the wedding. Its 3 years later & in July he had his 3 week military drill. He didnt mention to me that she was going to be there but I am aware that there will be times he'll drill with her unit because thats just how it works, so of course I didnt ask because I try not to interrogate or start drama. I figure if theres something for him to tell or something happened, then the truth will come out. I just let him be a man and take his word until proven otherwise. So today she texted him & my intuiton immediately told me it was her because I recogized the area code. She goes "Hey (my husbands last name) did u have drill? I thought we were gonna drill together this weekend." I asked him who texted him from that area code and he said idk someone from the military (as if I couldnt already see that myself) and i said well its a little odd that u dont care to ask who it is. Dont u want to know who your texting? And he said no because everyne in the military just has each others numbers I said okkkk thats fine but at this very moment doesnt it matter who you're texting and he said no. So i left it alone. Knowing it was her I didnt say anything. Finally I said who is it & he said her last name. So she responds again saying "Aw man, you should come up here for lunch." Meaning the military base. From what I know he hasnt had any phone contact with her aside from the very first time. He asked me if there was anything I wanted to know or she should say and I told him we'll talk about it a little later because our 2 year old is around and honestly i am expecting again and didnt want to be upset. I noticed the text was deleted and i asked him what else was said and he said "Oh i just asked where my book was" (I guess some guy borrowed a book from my husband). I said forget the book. Why would a random woman who u have history with think it's ok to ask you to come to the base for lunch as if you're just gonna leave your family to see her? He says he doesnt know and that maybe she thought they got "extra cool" at the 3 week drill. I said why would she think that? Because even in having casual conversations a woman wouldn't take it that far I hope. Esp if she is fully aware that you're not interested and have a family at home. So maybe the extra cool meant she thought YOU were interested. Idk. So he kept apologizjng saying hes sorry if the random message seems like something and that it really means nothing. Part of me believes him and part of me doesnt. It could be pregnancy hormones and I am usually really forgiving. But something just kinda feels off. Its not like this is a random woman. This is a woman who he was interested in in the past. And after all this time because she "probably thinks they got extra cool" she texts him because she happens to be drilling here this weekend. Im not really buying at this point. Should I just wait it out and see if anything else comes out or what?