Why is he holding back? Is it because of his girlfriend?

[Anonymous]

I have an going flirtationship with a colleague. We get on really well, have loads to talk about and have a laugh together as well as tease each other a lot.
I have caught him eyeing me up and then looking away when I catch him.
He slid into my DMs and we have been chatting but he suddenly stopped replying.
He tried to hide from me for ages that he has a girlfriend but I did find out the other day when he had to admit that he has a 'sort of girlfriend'. So I'm wondering if it's ti do with that?

[coldmarch]

It can be the cause, I've found that several men initiate some light flirt while being married or taken, but then hold back if things start to get more "serious", because they want to still feel like if they have freedom to get all the girls they want, but then don't want to actually go with them. However, sometimes this balance breaks and they actually cheat because have a small responsibility sense / severe ego issues etc.
So take this already like a red flag. If he is likely to cheat on his girlfriend and purposely hidden her to you, then you're already seeing some worrying traits of his personality. If you'll get him while he is still with her, or even worse, lies to you about breaking with her, you'd get a cheater and a liar and you'd be at the same risk of that girlfriend (no matter how passionated / attracted he can be about you, that will fade after a while and his personality will emerge). So the best scenario is that he was just "playing" because things are going very bad with his girlfriend and then he will close with her before restarting flirting with you. That way you'd get green light and he'd prove good traits.
Regarding not replying to text, anyway, this might be the cause but it could be anything else. He wants to hide messages to his girlfriend and so doesn't start convos, he doesn't want to get more personal because of not getting into real temptations, he was busy, he was distracted by something else then forgot, he thought the conversation was finished because you did very shallow small talk, he felt exposed and doesn't want to start mess between you and her, etc. It could be anything. But anyway stay alert about those signals to understand if it's actually a good idea to target this man. The fact he hides his girlfriend might be already a bad sign. Unless he is excessively introverted/reserved and really never talks about his personal life with colleagues, limiting everything to just job talks.

[Wise4myage]

His girlfriend busted him, but why waste time on a guy who's taken?

[In_Trance]

probably