Originally posted by Ah Ma:
If you are a guy, you have a girlfriend now, then at your workplace, you met your ex girlfriend who dump you because of work 2 years ago and you have spent 2 years to v hard forgt her. This ex girlfriend has then become your colleague & mostly u 2 spend alot of time working together nwadays & one day she confess that still likes you & jio you.
You know that you already have your girlfriend & have been telling yourself to be with your present girlfriend and forgt about your ex girlfriend by ignoring her but you just canot stop caring about her. Then realised that you still canot forgt her & still loves her.
If you are that guy, will you continue with your present girlfriend, or will you break with her & be with your ex girlfriend?

Don't worry Ah ma, this isn't very complicating, yet. Ok time for another lengthy post.
I am going to divide this post into parts which will let you see clearly why this isn't too complicating like it seemed to be. All he needs is a time to reflect, ponder and consider carefully.

His problem is attacking him into 2 areas
I) External factors - ex-gf working same company.
II) Internal factors - he discovered this new-found liking.
Basically, I do not know what causes them to break-up in the first place, but since you said she dump him (and you chose the word 'dump') therefore I presume it wasn't a good closure of the previous relationship. Trying hard to forget is NATURAL and the process of trying to leave an old relationship for a new life.
When she worked in the same company - they spend much time together. This triggers the feelings - chances are, its never liking UNLESS he admits that this present gf is a substitution for her. In love, we fell for a number of reasons - two of them were found here - time spend and begining-similiarity.

Beginning similiarity is a love psychological behavior of sourcing out characteristic that is similar to you and together with long time spend - it attracts. This attraction is very familiar because its the same vibes that draws them together the previous time.
Now she wants him back, there is two things I would like to point out:
I) She is the one who 'dump' him - now he is leading such good life, he should go ponder why he should end this 'good life' he is leading now for something he made him fall into misery and left. She came into his life not when he was the lowest point, rather when he was all-well and easy. Her present gf? During his road to recovery - & this is nothing to do with the arguement of responsibility and not love. Rather this is a fine example of compatiability, suitability and such.

II) He and her could get along so well without much conflicts is because there is a colleague status. I am pretty sure (85%) - that outside work, there is little similiarity and personality harmony. If he quits the job (like what Bear has mentioned), and try dating her, when the feeling dies, you understand why.
In love, outside responsibility, we need to know whom are better off when together in a relationship with us. In simple, the compatiability. I have one very good question to ask him:
HE SO SURE HIS FEELINGS TOWARDS HIS EX IS DEFINITELY LOVE? I don't think he knows for sure - and he is pressured subconsciously by her chasing as well.

P.S: When you have more choices to choose from - you look not at the facts and figure presented to you, rather you look at yourself and ask what do you really want.

Cheers