First off I don't have much experience here, but it sounds like he is doing exactly what I was doing to a guy I fancied when I was in the closet, so I would say he sounds pretty interested! Having said that, it also sounds like he might still be a bit scared of the consequences of anything happening i.e do you know if his wider family know/would mind if they knew he was gay? So just take it really slow and steady, don't push him too far but definitely hint you are interested! Informal dates are lovely, but try to focus on developing your relationship with him, not just going somewhere and then heading home (although I am sure you don't need me to tell you that!) maybe you could try to develop his trust in you by opening up to him in private about your own sexuality - rather than just hinting - as then he might feel more comfortable doing the same to you.
Also, please don't take this the wrong way, but it sounds like Michelle is quite a force to be reckoned with! You have already said he doesn't get along with her and it sounds like he might be worried that she would try to involve herself in your relationship with Zak and he probably doesn't want that to happen. Maybe you could try to show that YOU are taking an interest in his life, and it isn't just Michelle trying to get involved (I know that comes off as being really harsh to Michelle - I really don't mean it to! - it is just that in the way that you described her, she seemed to come off as a bit overbearing and motherly).
Again, I don't know you guys and don't have much experience here, I am just trying to offer my opinion from what I have picked up from your thread, so take everything with a pinch of salt and make your own judgements as I don't know you guys or your situations properly enough to make an informed decision for you!