I don't understand

why is it a relationship so fragile?
Things change within split second or rather, at the tap of buttons :x

I'm not talking not solely about BGR but also friendship/colleagueship.
I have this male colleague in his 30s (married with kid apparently). Lets call him FF.
Pls. if anyone going to think that he have a crush on me or vice versa, go bang wall!

Anyway, I was quite close to him for the pass 2 weeks or so. you know, lunch together, go for break together, bus home together (he stays near me) and even arrange to go out with other colleagues together. I did not fell for him like I aforesaid. He's just like a gurdian to me at work.
Someone to laugh with and talk to, becuase I'm still relatively new in this org and hence, I dont talk to a lot of the folks here. I really appreciate this new friendship.

However, things changed yesterday afternoon. Morning was still fine despite after me complaining about how lousy the way his cousin works. We still arranged to go for lunch together with the others @ 1pm. I'm not sure whether if its the following event that changed his attitude towards me.

Jon (my bro) texted me informing that lunch will be @ 12noon. I checked with him if he's going with anybody else but he said no. So, I asked FF if he could come with us for the 12pm lunch but apparently he can't and so I, out of goodwill, checked again if D is lunching with him.
conversation as shown below:

Me > FF: Jon say lunch @ 12. you can go?

FF > Me: cannot ley....

Me > FF: ok lo.... then later I go with him. D eating with you?

FF > Me: your wish.

Thanks lor.... I know i flew him aeroplane but I tried to make the best of both world. Not saying that either will die not lunching with me but I don't like to eat alone and so, I make sure people around me won't dine alone if it concerns me. get what I mean?
I tried talking to FF after I came back from lunch but all I get was sarcastic replies. grrrrrrr.
I attempted to be more diplomatic. Oh well.....

I psyched myself into thinking that he's probably having a bad day at work or too busy to chat.
Obviously not. He just didn't want to talk to me. He's still giving mt the cold shoulders today.
fine with me. I shall leave him as it is and get on.
It's sad but my world don't revolve around him and I'm just here to make money.

Hope things will get better thou.