Everyone has a type. Whether it be tall, nice eyes, huge muscles, or a great personality. But what one may not know is while some may be more open to different forms of that type, others can soon become more familiar once they have found a type they really like.
Okay so it's been months since you and your ex have split up, and you recently became aware of his new girlfriend or what others are calling your long lost twin. Believe it or not, this situation is not uncommon. Many men are known for dating a doppelganger of their exes. Once a relationship ends, men like this are more prone to find a more "upgraded" version of what they had before. According to Therapist Dr. Bethany Marshall, dating look a likes of past lovers can become unhealthy. By sticking to the features of one particular person he is replacing that person rather than starting fresh which does not give him any room to grieve nor make room for an attachment for the new woman in his life.
They say imitation is the sincerest form of flattery so yes you should be flattered. Regardless of how it ended he's expressing that you meant a lot to him if he is willing to be with someone who looks exactly like you. If something is over, especially if it ended bad, one would think they wouldn't want any reminder of that situation. However if you have any reservations to have this person back in your life remember he is an ex for a reason. No one knows the relationship you had better than you so look back before putting him back into your future file.