I guess it would depend on how he is talking. If he is just commenting respectfully about another girls looks, that is normal. If he is being disrespectful in his way of commenting then you need to tell him that is unacceptable. If he is talking about past relationships again it depends on what exactly he is saying. I believe he can love you and still talk about other women. Just ask him to stop and if his love is true he will.
He could be testing you to see if you get jealous easily but he could also be trying to break up with you in a very jerky way. Ask him why he keeps talking about other girls all the time.
Does he do this on a daily?If he does than he has no respect for you and you should dump him.If he was in love with you a thought of other girl's should not be on his mind.