When you're seeking advice consider the source. If you want ongoing support for your relationship you need someone who understands clear boundaries, expectations, and communication. If they can't do it in a professional setting, be sure they can't help you learn to do it in a personal one.
Find someone with clear professional guidelines they follow. This helps them be sure they can support you without getting tangled up in your (or their own) shit.
I outline my boundaries on my website, in contracts, in initial sessions, screening calls, and by following the ethics codes of two professional organizations. If you're hoping to work with someone ask them about the boundaries of their work.
Find someone with lived and professional experience related to whatever topics you want to focus on. Lived experience helps them have empathy and deeper understanding. Of course, if they have solid boundaries they're not going to use your time to go into great detail about their own stuff- but you can ask if they've experienced similar struggles.
At the same time be sure they don't ONLY have personal life experience, but also PROFESSIONAL experience to back up their work. There are far too many opinionated "experts" who just want to teach you the way they do relationships who don't actually know what they're talking about, or how to help you. Hire someone trained.
You can ask them about their experience- or better yet, ask them how many folks they've supported (professionally) who are working on the stuff you want to focus on. If they haven't had much experience hire someone else, you're not here to train them.
Lived and professional experience is critical, but they are two of three critical pieces of this work. You also want someone who has studied or read a few things to back up whatever they're selling you. Ask them what books, teachers, research, and training they draw from when they work with people. Be sure you hire someone who knows what's up.
Ask to see proof their work actually, well, works. Do they have testimonials or data that shows they're good at what they're doing? You don't want to hire someone who over-promises in an inauthentic program, but you need to know what to expect. Ask how they measure success in their work.
Finally (but probably most importantly) it is essential you find a professional who takes a non-judgmental approach. Far too many therapists, coaches, and healers come to the table with their own biased agendas that will compete with your needs.
Are they pushing non-monogamy? Do they believe monogamy is the best path? Are they really shame-free about sexuality? If they've got hang-ups in these areas they're going to carry over into your work.
If you can't say things to them for fear of judgment, shame, or criticism, please please please hire someone who can set all of that aside and meet you with clear presence.
Thanks for reading through my rant. I get protective of my clients and see far too many people who've had negative experiences with couples therapists, marriage counselors, and sex educators along the way. It's super risky to reach out for help- I hope this helps you discern a solid fit for your vulnerability work.