My exploration into gender over the years has sometimes gotten me into hot water with some people because the lines can be fuzzy. In the past we made very clear distinctions between people who were transsexual and those we termed transvestites but as Harry Benjamin showed us in the mid-twentieth century with his extensive patient history, there was a blurring as one moved up his scale.
The reality is that this is a very complex topic but one thing that seems to stick out as a differentiator is the presence or absence of gender dysphoria which in its more extreme forms is what drives a person to transition in some way (be it social or medical). If you aren’t dysphoric then it’s a good possibility you may not be trans.
The act of cross gender expression can be as benign as something which relaxes a person or as significant as the early exploration of a trans person on their way to a full transition which is why it is so hard to make diagnoses as to what an individual requires. For example, people who in the past have self-identified as crossdressers may suddenly find years later that there was much more than met the eye and successfully transitioned later in life (my recent posting on Petra Wenham being one such example).
The conclusion that I have come to in all this is that fundamentally we should do everything we can to support a person in being happy. If harmless cross gender expression does that for them (there are loads of happily married men who crossdress) that is great but if it extends into the area of gender identity, we should help the person attain their goal through whatever means necessary.