Why is my Ex so nice to me all of a sudden??

My ex (who is also my co-worker) broke up with me 3 and a half months ago because he thought I cheated on him but I never ever did. During those 3 months we did speak at work only but it was strictly work related conversations. Every time I’d try to bring up us talking about our relationship he’d shut me down. All my calls text messages emails etc though out that time he never responded to them.

Now since the new year has started our conversations switched from worked to personal/ friendly type conversations. Also my birthday was recently and he bought me a gift (a really nice perfume that I had mentioned to him while we were together that’s is really expensive and he bought it for me for my birthday) Plus he gave me a hug and a kiss on my cheek!! So jokingly I texted him that I’d prefer it on my lips and he said okay I coming back. ( but that didn’t happen though because we were at work)

So since we were having all this friendly/ old times sake chats I figured that on my birthday I’d ask him if he wants to hang out and his response was “ do you think that’s it wise for us to do that?” twice. and that I dont want t stress you out on your birthday

So now I’m confused why talk to me so nice for hours on the phone but now still shutting down my advances??

What does this mean? Does he just want to be friends again??