Okay, this is what you need to know. About 50% of guys would rather die that wear any women's clothing. For them its just a torturous form of humiliation. Then about 40% of guys will cross-dress at some time in their lives, but only as a joke. They think its funny, and they enjoy shocking our sensibilities. Finally about 10% of guys will cross-dress and really love the experience. Are these guys crazy or what?
No, for the most part they are just normal, healthy, heterosexual (yes, about 90% heterosexual) males with one little kink hard-wired in their brain. When they feminize themselves their brain responds by releasing dopamine and other neurotransmitters. These neurotransmitters produce sensations of well-being, pleasure, sexual gratification and self-identity. It's a fetish. Its a common fetish. Its just as if his brain is interpreting cross-dressing as contact with a female. It affects the reward centers of his brain, so it brings a strong sense of gratification, and it does mimic the addiction response.
Many of these men recall that as a small child they over-valued females - thinking girls were valued more in society than boys. When they cross-dress and they feel those sensations, it brings them comfort a sense of being "okay", and pleased with themselves.
Many men start cross-dressing as teenagers and experience sexual gratification, and stimulation. Then when these same men get older and cross-dress, it is no longer a sexual thing, now it is more for relaxation, comfort, and a sense of self-identity.
It truth, they really don't love to wear women's clothing. They just love the sensations from the release of neurotransmitters. And, they are using cross-dressing as the tool to get their brain to release the neurotransmitters.
Most psychologists do not consider cross-dressing as a problem, as long as they still function normally in society. So as long as they set their own limits and keep it private (in the home), it is no big deal. Of course, it does mimic the addiction response, so he does need to keep this under control, or it can take control over him.
Don't encourage it. Don't discourage it. Just let him know that you love him just the way he is, and you alway will. Most men consider their cross-dressing as a problem - it make them feel guilt and shame. So it is really hard for them to share it with you. So when he talks to you about it, it means he trusts you, and he considers you mature enough to handle this. Great.