Pisces at work

I had worked at a company for nearly 3 months, there was a Piscean who was a senior colleague to me, and I was sorta an assistant to him, he gave me assignments, I wasn't attracted to him physically at all, after a while I couldn't help but noticed that he treated me particularly nicer than others. After the job was terminated, I texted him the next night, saying that I'd like to thank him for being so patient with me and took care of me, and would love to invite him to have a dinner with me, he texted back and said that I was helpful, therefore we went out the another night. I would hate myself if I didn't get to say goodbye to him, that's why I got up my nerves to make the first move.
He is definitely the most sweetest person I've never met, I have come across with several Pisceans, no one can compare to him at all, he really cared about my feelings, asked me if I got used to the working atmosphere, always looked me in the eyes (Somehow I couldn't stare at him that long.), would teach me things patiently and corrected me quietly if I had done something wrong, there was one time he stood up for me when another colleague treated me in an unfair way, he often called me when he was out meeting clients and taught me things via the phone. Does it hard to get Pisces' trust? He asked me to answer his incoming calls while he was having a 4 hours meeting (He regularly let it rang), I mean cells are so personal, he let me possess his cell, it was kinda a big deal, wasn't it?
I think it might be different to tell what he thinks 'cause we meet through a workplace, I considered him as a bubbly and sensitive person as what I've observed. However, it was a bit weird over the dinner, he talked most of the time, it was like he lectured me professionally and personally, he barely smile that nite, kept a straight face the whole night. I probably looked bored after all those lecturing, he mentioned his girlfriend a couple of times, and told me that he was planning to get hitched with her, did he bring her up just to remind me that he's attached or w/e? Why did he change his attitude towards me after I left the company, and apparently he was hiding his feelings.
Nearly all of friends think that I'm reading too much, he just treats me like a lil sister, except a Scorpio and a Cancer friend who also feel that he's interested.
Btw I'm a Libra, he's attached to his woman more than 4 years and his moon sign is Cancer.

I tried not to give it a lots of thoughts, nevertheless there were certain of colleagues who told me that he never treated anyone that way ever. I dunno ppl kept saying that he was cheap, he never bought anything to his co-worker, he bought me a drink and snacks several times.
And I didn't think that I expressed my true feelings that much, I do somehow look cool on the surface.
I'm aware that he's attached, he is such a great mentor, I wouldn't mind keeping in touch with him or should I? I do look up to him at work which he was fantastic in it. The main reason of the dinner was to appreciate his kindness, I honestly told him that "You're really great." He was like "No, I'm not nice" it was awkward, I didn't know how to respond to that. Are Pisces suckers for compliments? Anyway I've found a new job, should I inform him the goods news? I really don't want him to think that I'm into him or something, is it possible to have a purely friendship with a Piscean.
When Pisces are in a stable relationship with someone, would they still consider some of the opposite sex as friends and keep seeing them 1 to 1?
I would like to know how Piscean reacts that way from the perspective of Pisces. Pls. weigh in.🙂

Adrienne if he says he's not nice believe him but for the most part I think he was being friendly and in return you stroked his ego and what man with a bit of power doesn't enjoy female attention and ego stroking, so his being nice was more for him than it was for you. Sometimes when someone see us struggle or someone reach out to us and fill a void we automatically begin to assume the best and pedestal the person especially if a woman doesn't have a satisfactory dating life or a history of being with neglectful men she tend to get swept away by a bit of male attention and read too much into it, huge red flag is when he told you he's not nice and he has a girlfriend he plan on marrying, that for me would make me stop thinking of him as an available option. I have a feeling your into him and your masking it as friendship thus all the questions, I don't think anyone here is going to promote you chasing a guy that's in a 4 year relationship with another woman, he's not available so in lack of a better word move on.

You can chase him and see if he bites but be ready for rejection through out the process...

I know Libra's in general hate to simply cut things off at the ankles, especially if there was a great friend/work-relationship present. I have the feeling he IS keeping you gently at arms length now (even saying he's not so nice, that he's getting hitched, & his rather platonic lecturing convo's; all tell-tale signs). I'm thinking he is more comfortable and secure in that working environment he had with you, especially now, since there are no longer any bounderies. It was really nice of you to think of him and thank him for mentoring you, a pisces "would" appreciate this and not forget anytime soon. However, he may read any further contact in a different light, that he may not feel quite right with, considering his status. Aside from friendship, respect alone from a Pisces is nothing too shabby either.