I (M25) found out my partner (M26) was messaging another guy. Is this emotional cheating and how do we get back to a place of trust and intimacy after this?

Me and my partner have been together for about 5 years and recently I found out he has been messaging with another guy he met online from another country. They mostly were just talking about life stuff but the other guy would make sexual comments and flirtations towards my partner (calling him sexy, saying we should meet up if you ever visit the UK ;), and asking if he had his dick out) and my partner in turn either ignored it or just said no haha. The worst my partner said was he could tell the other guy has been working out. When the other guy asked who he lived with there was nothing about me said. They did not trade any nudes now but they have in the past years before me and him got together.

My partner claims that he’s been feeling lonely having moved away from his friends (which is true) and that he just wanted a friend and was overlooking the flirtations because it was nice to talk to someone. That being said he admitted if I walked in the room he would have closed the messages. I am not sure if I feel like this is cheating and wanted to get other opinions