What is his deal and how should I proceed?

[Eviedreams]

My ex and I broke up over 9 months ago, he left me after I wrote him a series of nasty texts (at the time I felt I was driven insane by his irrational behaviour in our relationship, I am not proud of it but I do feel it was provoked). I apologised a lot but he remained cold and distant, proceeding to insult me on his social networks (indirectly) a few times after we broke up. My heart was broken but I managed to move on.
Then we found out we are going to be the best man and the maid of honour at our friends wedding. I instantly started worrying. If he hated me so much he would call me things on the internet, how would he act now? We had not spoken since the break up when on Thursday I received a text from him, friendlier than ever, asking me to practice for our special song (apparently there is a special song for him and myself). He admitted to being a terrible dancer and knowing I had a good sense of rhythm, he wanted to ask me if I would help him practice. I just thought it was weird he would be so nice to me, but then again, he highlighted he wanted us to act nicely to each other for our friends.
So I said yes. I needed to see him and break the ice before the whole wedding thing starts.
We agreed to meet at his friend/s house as he has a nice big living room and nobody was at home. He was super nice - and then things got weird. I first mentioned my dress would be knee-high, he proceeded to comment he is sure I will be a very beautiful maid of honour. Then I told him not to spin me too hard on the dance floor as my dress would go up to which he commented he wouldn/t mind, but would even like it. Then I asked him if he booked his room at the hotel we are staying at, to which he said he wouldn't mind sharing the room with me. This is the man who apparently was heart broken and shattered by my behaviour (I won't get into that story now), who cared so much about me and I broke his heart. Being nice is one thing, but this was.... confusing.
Was he flirting with me? Or was it just joking? He also implied he expects to dance with me a lot that evening. I also contacted my friend (the bride) and she said there was no special song for him and myself.

[Jerome]

I don't think he is joking, however, make sure you don't act too clingy or desperate to be with him. Simply act as a friend to him, because doing otherwise will turn him off. If you act act a friend to him, he might consider getting back together with you.

[Julia]

I think he still loves you, even though it may appear that he was flirting with you. I will advice you act cool around him, and don't show off your feelings. Don't be the one to initiate contact or anything else, let him be the one to do the work. That way, you will appear more attractive.

[Clinton]

These feelings are quite normal after experiencing a breakup. You may not know how to move forward and let yourself be happy again. The first step towards moving forward is to know how to remain cool around your ex boyfriend.

Dress Nice
Now that you are no longer together, it is time to focus more on yourself. Go ahead and dress nice and leave him speechless. Once he begins to notice how confident and put together you look, he will be quite shocked. This will leave him with a lot of questions going through his mind.

Stay Calm When You See Him With Another Girl
As much as you may want to scream and get upset that he is with another girl, keep yourself calm. There is no reason to waste your time upset over someone who did not care enough about you. Continue on your way and act as if it does not bother you one bit.

Relax When You're Around Him
If you happen to run into him while you are out, don't be afraid to be near him. Just because he is in the same place, does not mean you have to leave. Hang around and enjoy yourself, and just ignore him.

Look Happy
Being happy around your ex boyfriend is the best way to act. Show him that you are much better off without him in your life. He more than likely wants you to be unhappy, which is more of a reason to be happy!

Think of Good Things
Avoid thinking negatively, but instead try to stay as positive as possible. If you are thinking too much about the past, it will show up in your expressions. Don't focus on what went wrong between you and your ex boyfriend. Let go of the past and move forward.

Be Cool Around His Friends
Not only should you stay cool around your ex boyfriend, but you need to also stay cool around his friends. Friends will always talk to each other, and they will let him know how you are acting. If they are letting him know that you act like you have moved on, than he will start realizing that you have.

Make Him Feel Like You Don't Need Him
Show him that you have moved on with your life, without him. You do not need him in your life to be happy or succeed. You can do this all on your own, independently. Make new friends, and enjoy new experiences with new people.