He sounds like an idiot for starters. If he doesnt love his wife eventually the children will see this and they will not have a good example for relationships. Maybe he does love his wife and is just telling you that. Some people unfortunately when married think having kids will improve the marriage. So very wrong it only complicates things. Then others have a loyalty feeling or financial limits that don't allow them to leave their spouses if they are unhappy. So the live two lives. I myself would not want to be sloppy seconds to anyone and you shouldn't either.
AnswerIf this is a married man saying this to a female other than his wife, I would be very suspicious of that because it probably is a lie. He is minimising the relationship in order to either cheat or keep his lover (who he cheats with) on a string. If this sounds like you, I would get out fast. He isn't going to commit.