Boyfriend cheating?

I've been in a long distance relationship with my boyfriend for a year now and I found out few weeks ago when he came to visit that he was talking to two other girls, flirting and calling them names like "baby"...
We talked about it; he said he don't know why he did it and that it was a mistake so I decided to give him a second chance but I can't stop thinking about it and I'm scared he might do it again. 
Can anyone give me any advices please? I'm really confused...
Thanks.