Is this considered cheating?

So I just found out that my husband has been talking to a girl he use to hook up with before he met me. The husband of this chick, texted me and sent screenshots of some of their conversation. In all honesty, she was the one instigating it all, but of course, my husband replied, so he is definitely to blame for egging it on. The exchange was flirty, and the worst part was her saying she still dreams of his… you know.. and his reply was, “I still have it… :)” they said it’d be nice to see each other in person, and that they missed one another. The husband of the girl also stated that he found out that the two of them had met up in 2015 and had sex. My husband of course denies it, and I have no proof whatsoever, only screenshots of one small conversation. So, I know this is inappropriate behavior, but do you think it’s crossing the line cheating, enough to leave him over?