First of all, congratulations on your engagement Is that your ring in your avatar? If so, it's beautiful!

Next, I don't think there's anything wrong with you at all. This is all to do with the ex boyfriend. The way I read it is that he's trying to manipulate you by playing with your feelings, telling you things he knows will piss you off or upset you. That is just not on. He seems to have some kind of need to hang on to a little piece of the past with you by bringing up something that he knows will hurt you.

My advice? Walk away from him. Leave it in the past. Let HIM deal with the fact you are going to marry another man, and don't let him manipulate your feelings anymore.

We all feel a little bit of pain when ex's get together with someone who should be out of bounds to them, but why did you need to know? Why did he choose to share that with you? He could have kept it to himself and you'd have been none the wiser. He told you because he wanted a reaction, wanted to set your mind racing, wanted you to remember the times you had with him. Don't let him do this to you, you're worth so much more than that.

I feel I might be sounding a little hard on him, but my sister was under the spell of a guy like this for a long, long time and he caused her years of pain, just by not allowing her to fully let go, by turning up when she least expected it, totally manipulating her, and I had to watch him do this to her. As far as I know he still shows up every now and then 'for old times sake'

Like I said, it is normal to feel a twinge or 'something' when faced with the news you were given, but his reasonings for sharing that with you can only be malicious or in some way to make you doubt your feelings for your fiancé, make you doubt yourself, your own feelings - something. He shouldn't have told you. Walk away, and enjoy your life with your new current man. Let the ex wallow in the memories of what he's lost

I wish you a happy engagement and a wonderful future with the good guy