My opinion is that attending such an organization may prove to be more of a waste of time than real benefit. Now don't get me wrong as I'm not slamming the organization as I really don't know a ton about it. However, in your OP you basically stated that you need "human contact." The problem I see here is that you, I, or anyone else needs
quality human contact. I would rather spend time with just one or two people who accept me than "branch out" among people with questionable intentions just to have a lot of people around.
I know that that is not what you are trying to do but it also seems strange for your therapist to be making what appears an unreasonable request on you. If the trans community is distant from where you live, then obviously you are not going to be able to be heavily involved with it so I don't know why your therapist is insisting on this. I certainly agree about needing human contact but some of these things may just take time. Perhaps I am fortunate because I live in a very large city. Even then, there aren't exactly trans people "everywhere." Even most of the nightclubs I go to that are GLBT often have 0-3 other TG people there so it isn't uncommon for me to be the
only one. Regardless, I won't pass up the opportunity to meet heterosexual couples and other non-trans people who do accept me for who I am.
Anyway, here are the reasons I don't support spending much time (let alone money) with Tri-Ess. The first is that for the most part the group is exclusive. Right off the bat this means they won't help you or will provide little help if you fall outside of their inclusive requirements. Barring a few local chapters here and there, the group is dedicated to heterosexual crossdressers. This type of exclusivity seems counter-productive to any meaningful support of trans issues. First, gender identity and sexual orientation are completely separate issues. Excluding homosexual and bisexual crossdressers from the group is blatant discrimination and to me is as intolerable as if it were a group for only Caucasian crossdressers discriminating against race.
The second issue I have is with the excessive focus on crossdressing. Most trans people don't consider their dressing to be "crossdressing." I know I don't consider the way I dress to be a joke or some fun activity. While I'm not full time yet and have limited my dressing to mainly GLBT environments, the clothes, makeup, etc. has become second nature. It is not about the clothes, it is about how I indentify and feel comfortable. I don't consider myself any more of a man wearing male clothes than when I wear female clothes. The clothes do not define me. Also, the group's name "Society for the Second Self" is misleading on trans issues. While it may work perfectly for androgynous people or crossdressers, transsexuals do not consider ourselves to have "two selves." We still may not conform 100% to gender norms within our preferred gender role (even TS's can be somewhat androgynous) but we generally consider ourselves to be of one particular gender or we wouldn't transition.
The concept of crossdressing basically sounds like an activity, an event, or a hobby and that is generally what Tri-Ess appears to be about. Groups of men (who identify as male) disguise themselves as women and try to pass in public. They then go back to their male life when the fun is over and don't plan on transitioning. As several others here have stated, the moment that a member of the group decides that their crossdressing is more than a game but is instead a gender identity issue, the group is not interested in supporting them.
Anyway, it is up to you. For me, I don't need a group to teach me make-up, clothes, walking in heels, etc. It may be of some benefit but such benefit is very short-term. When I go out in public I want to be seen and treated as a female, not a crossdresser. So to be completely blunt, if being transgender is something you take very seriously, I would focus on groups (if they are available) that are actually dedicated to trans issues in a serious way. By serious, I mean the discussions will frequently be on things more important than shopping for outfits.
Good luck.

Britney