Your girl/boyfriend might be over them, but you sure aren't. Exes are horrible because no matter how hard you try to forget, they will always have gotten there first. Yeah, you have them now and you should try to focus on the fact that they love you. You should try to get over the fact that their bits have already smushed into someone else's bits. Nothing your boy/girlfriend says can help you get over that fact, you just have to convince yourself that you've won and they can go suck it, not your boyfriend's penis, someone else's, that is...
'It was never like how it is with us.'
So what was it like then? Just sex? Deep enduring love? Total ambivalence? Not to generalise but guys don't usually like discussing feelings and awkward discussions about past relationships are right up there with topics they'd rather not discuss - along with 'where are we going' and 'tell me why you love me', or even 'how is it with us?'
'My ex was never into that.'
Whether this is a positive response to some interest you're into (like you and your boy/girlfriend both love the same show that their ex hated with a fiery passion and they are happy they can share that with you), you can't help thinking: 'well what were they into then?' You can't help being curious about them, and their Facebook page can only tell you so much.
'We're just friends now.'
Can you ever really be 'just friends' with someone you had sex with? How can the first thing that comes into your mind when you see them not be 'I had sex with you'? If you broke up because you didn't make a good couple, why do you think you would make good friends? Where you even friends before you were together, or was your initial interaction of a sexual nature? It's great when you can be friends with an ex, but why would you want to? As a safety plan?
'You're really nothing alike.'
So how were you attracted to them? If you're attracted to me, there must be something that we share in common, besides our genitals. This can be worrying if you know that they are really different to you, in fact, they are so different that in no universe would you get along with them. Yet you both have the same interest in sex partners? Also, will you ever really be able to shut off the voice in the back of your mind that keeps asking if your boy/girlfriend would change back to wanting what their ex gave them (unless it was the clap).
'You're both so similar.'
This is way worse! We are so not alike and if we are, does that mean that your girl/boyfriend has simply replaced their ex with an updated version? So are they in love with you or a revamped better version of their ex? This especially sucks if you dislike their ex purely as a person. Why would you enjoy being told you're like them?
'You're so much hotter.'
That's true, but is that really all you care about? Does physical appearance trump having an actual personality? Really? Good job trying to romance me, jackass. But thanks.
'I would never get back together with them.'
I'm sorry, was that even an option?? Why would you even bring that up? Is there a small voice inside your head that's considering them as a backup? Does that make me plan B and them plan A, because they were there first? WELL?
'She actually kind of sucks.'
Your penis?? The life out of relationships? Blood out of your arteries? Be specific or my mind will turn your ex into the monster that I want them to be. This makes it more legitimate for me to hate them. Totally justifiable to call them a bitch if I have evidence to back up that statement.
'We were never serious.'
Whether it was a one-night to end all one night stands or a fully-fledged relationship; they mixed bodily fluids and emotions, which is the real issue here. If you wouldn't have got along with their ex anyway, this makes the fact that they slept with your boy/girlfriend before you did, that bit more difficult to swallow (unlike their semen hey-o!).
'OK, shut up. I fucking love you, you daft clown.'
OK. I get it, you love me. Cue gooey feelings inside. Because even if their ex was there first, you're here now and your girl/boyfriend chose you and you chose them. So their ex can suck it! (Again someone else's dick, not your boyfriend's.)