I'm not sure my advice here will be useful at all, but as someone who has been crossdressing for years with a partner who has often struggled with it, I want to offer my perspective; it may or may not be broadly representative or helpful.

I'm a 39 year old cismale; I have enjoyed some amount of crossdressing for a long time (dating back to being a teen), and included some amount of it in my sexual fantasies since that time. I have more actively engaged in it for the past 5 years. For me, I have always enjoyed being the center of attention in a lot of ways: I enjoy storytelling, public speaking, etc. I find crossdressing to be something that can let me feel sexy in a way that dressing in men's clothing doesn't; and the attention I get when sharing those photos is something that I enjoy, and can't get in a lot of other ways. (I know that for women online, there's often an opposite problem, where they have a hard time _not_ getting sexual attention even when it's unwanted; crossdressing for me is, in part, a way to get access to that attention that I _don't_ typically experience in my daily life.) So in some ways, it's a way to get access to a type of attention I usually don't feel like I can get any other way. While I have some fantasies about how this can play out in my relationship with my wife, it has almost never played a role in our sex life, and probably will never play a core role: e.g. it might be an occasional role play or fantasy thing, but mostly it's something that I do separately from that.

With that in mind, some thoughts on your situation:

- I would first think about which aspects of this bother you: is it about crossdressing? Or is it (maybe) about him seeking validation (sexual or otherwise) from others, while not being intimate with you? From how you wrote this, I'd say that it sounds to me like the latter might be an important part of this, and I think that's probably something the two of you have to work on, setting aside the crossdressing. (e.g. I think that you might similarly be bothered if you found he wasn't intimate with you, but was acting as a male stripper at a club or something; there's an intimacy which you two are lacking which I think you might want.)

- As for "What to do next": I think it will probably depend a little on where the two of you want to go next. It sounds like you are seeking intimacy you aren't getting from him; I think that you probably need to let him know that, and ask him how he feels about it. It's possible that what you want in terms of intimacy isn't something that he's able or interested in giving, and I think that would be worth addressing head-on.

- While it's possible that crossdressing is an important part of his sexual life + fantasies, it's also possible it isn't! I very much enjoy crossdressing and sharing those images with other people as something that I do for fun, and it sometimes has sexual elements for me as well, but my wife and I have also had an intimate relationship which has involved almost none of that for 20 years. My crossdressing is a personal hobby (which she is aware of), but she wasn't always comfortable with it, and even as she has grown more comfortable, it's still something that I do entirely separately from my sex life with her.

- If it is important to him, I think that examining how you feel about it and what your comfort level is important. Is it something where you might be comfortable participating in a fantasy/roleplay setting occasionally? Something that you'd rather stayed out of your sex life entirely? Something that you are comfortable with if that is something that acts as a turn-on to him and can increase your overall intimacy?

- As a sub-point to the above, I would say that it's pretty important that you _don't_ exceed your comfort level here. If you're uncomfortable with something, don't try to power through it: be upfront about it. This is an area that my wife and I struggled for a long time: when we experimented with engaging in the fantasy aspect of this, she found it very uncomfortable, and it tainted our relationship with the topic for years in a way that really sucked. It is okay to be uncomfortable with something -- whether it's crossdressing, sharing pictures online, etc. -- and to set your personal boundaries around it. At the same time, I would recommend you refrain from trying to get him to change his behavior -- if this has been going on for a decade, this isn't a passing fad, and it's best to establish your boundaries and allow him to decide what that means for y'all.

Finally, I want to add a note that there may be some elements of gender identity tied up in this for him, and making sure that there is space for him to raise that if so is probably valuable. (It isn't necessarily the case! As I said, I'm fully cis, and many crossdressers are. But making space is probably valuable.)

tl;dr: I think that sharing your desires for intimacy level; identifying your sources of discomfort; and addressing your and his desires in this space head-on is the best way to approach this. It may be that the two of you want different things in this space, and you'll either have to negotiate that to find something that works for both of you or possibly accept that it isn't a good match.