Well that is a very good habit that you are thanking GOD. because people only tend to complain to god but never thank them when they achieve some thing. But yes you can not pray the god for a win in gambling 
Yes, because I feel that GOD always helps me anytime, especially if I have trouble or a problem. I can not stand until now if GOD does not care for me. Only thanks to GOD that I can do to feel grateful. I do not have to pray the GOD for a win in gambling 
That's a better approach, better always be thankful for basically anything that happens, also because anything can happen! Therefore, yes, keep praying if you really have to but don't forget that the outcomes of your bet are prayers-independent.
"Sometimes, GOD will allow us to win, but the other time, we will lose" that's delusional, sorry
I will still pray in any condition and situation. I do not think much about winning or losing in gambling because that will consider the luck that I can not predict. At least, praying in any situation will help me have patience and calm down and help me think."Sometimes, GOD will allow us to win, but the other time, we will lose" that's delusional, sorry