I'm so nervous! Do I just act normal?

Ok so today I have to into my ex partners work place to book an appointment. I haven't seen him since we broke up a 2-3 months ago, and we also haven't seen each other since getting back from our holiday abroad together. We were arguing a lot in the week after we came back, so much so that we didn't see each other (just had phone convos).
Around 2 weeks later I broke it off cause we couldn't fix any of the issues we had and I felt like I was the only one trying!
Between then and now I found out he'd lied about a lot of different things and he asked for me back not long ago. I said we could chat after a certain event he was attending (it caused us the most issues), he agreed and then I found out just a few days later he went on a date with another woman.
Also that he'd messaged back another woman who he was just sleeping with before me saying I'm the reason he hadn't replied as I didn't like him talking to people (she messaged him through our relationship and he didn't reply cause he was getting sex from me! Told me he was just using her for sex when we first got together and broke it off cause he had me now). He then didn't tell her the main reason we'd broken up as that'd look bad on him!
Anyway I messaged him saying i knew about the date and he got very aggressive and defensive. At a later date he went to his friends wedding which I hadn't been invited too when we were together and he made out with the grooms sister... then sexted her after to try and get her to sleep with him!
It didn't work... He doesn't know I know that part.
We left it on pretty bad terms as I caught him out with going on a date even after asking for me back so it's more on him. But how do I act if I see him? Just normal or really friendly or indifferent?
I'm so nervous! Do I just act normal?
Add Opinion