Have you talked to your own therapist about this? Since they're good about boundaries, they might have some input about whether you can be helpful in this situation, or if you should distance yourself for your own protection.

At my session last week I asked about bringing my boyfriend in occasionally for couple's counseling, because we both have things that we're working on, and she said it could be really helpful for me to offer a third party point of view on things that he may not realize and therefore hasn't been discussing with his own therapist. But with us dating it's different from a friendship, since we're already emotionally invested in each other.