My 30-year-old partner, who is 30 as well, is procrastinating on going to the dentist, and it's impacting our intimacy. What should I do?

I want to start by saying that I really love my boyfriend. We've been together for nearly four years, live together, and have discussed the possibility of marriage. That said, I have a concern: he hasn't visited the dentist in at least six years, and his dental health has visibly deteriorated during our time together. Initially, it didn't bother me too much; we both had areas to improve as adults, and dental care was one of them. I've started going to the dentist regularly every six months, but he hasn’t taken any steps, even though he has dental insurance he’s never used. Whenever I bring this up, he becomes noticeably upset. I express my worries for his health and emphasize the importance of addressing these issues before they worsen and become more costly. Despite making multiple offers to help—like scheduling an appointment for him at my dentist and even suggesting we go together—nothing has seemed to help, and it feels like he becomes more bothered each time I mention it. I try to space out my suggestions to avoid overwhelming him. Unfortunately, things have gotten worse. His breath has developed an unpleasant odor, and I often find myself turning away during conversations. Kissing has become less enjoyable, and after intimate moments, I frequently feel the need to brush my teeth and wash up to avoid lingering smells. Two years into our relationship, we discussed how his dental hygiene was a turn-off, and while he made an effort to improve brushing, it's not enough. I’ve communicated this to him. I genuinely don’t understand why this continues to be an issue, especially since we have insurance and can afford dental care. Admittedly, my motivation for intimacy has dwindled, which I believe is partly due to this situation. After having COVID last year, I’ve become more sensitive to smells, making this all even harder to cope with. I’ve brought this up with my therapist, who suggested that we try couples therapy since I’m finding it difficult to communicate my concerns effectively. Should I be upfront and tell him I’m grossed out? Would a couples session help, or could that come across as ambushing him? He can be quite sensitive, and this topic has upset him in the past. I'm unsure how to present the idea of therapy in a gentle way that won’t feel harsh.