To be honest there is no way to know what goes on in someones mind unless they want you to know.
Even if the ywant you to know you can never know that this feeling / thought / emotion will not change over time,
Old_Geezer makes a valid point , especialy in respect of sign's and time.
However even with this i would state that if you have to ask this question then you must have doubts even if you dont yet know or why.
When you trust someone completely you dont ask if they can be trusted , you simply do.
If you feel someone loves you , you dont ask if they do you simply accept it.
If you are not sure then you dont know and ask , however with something that involves someone's emotions / thoughts/feelings , you can only hope they can elaborate enough to share what they truely mean when answering your question.