I would like to help you with your question.
It is important for you to trust your feelings here. There is definitely something strange here with his behavior. His saying that he is in a long-term relationship and then 3 days later wanting to meet you for fun suggests that his intentions are unclear and that he may not be trustworthy. Perhaps he is not in a long-term relationship and just told you that so he could take more time to decide if he wanted to date you.
Maybe he has not dated much and was taken off guard by your request. And then he has been having others test and judge you so that he can build some confidence. If this is the case, then his approach (not telling the truth about his dating status and having others check you out) needs to be explained and he owes you an apology.
On the other hand, if he is in a long-term relationship then this is not a man you will want to spend time with because there is no future here and you are likely to be hurt and used. His using colleagues and perhaps his parents to test and judge you is hurtful.
His sending you photos is unsettling. Since you know who he is...you see him at the store routinely...there is no reason to send you private photos. There is a strong liklihood that these are sexual in nature.
Since you shop at the store with your Mum, you have some protection from him acting inappropriately. I encourage you to cut off all text and phone conversation with him as it does not appear that his intentions are pure. Next time you are in the shop, tell him to not contact you again.
With all the things you have stated in your post, it does not seem that this man is respectful or appropriate.
Let me know your thoughts.