Question for couples who have had threesomes

My partner and I (both women) were discussing the idea of a threesome with a guy since it’s something we might be into and it would give me a new experience. However, I’ve told her that we would really need to go over and address any insecurities and boundaries we have before we even consider this for real, because I know that could cause issues in our relationship if we go through with something like that. She’s worried that she might not be adequate enough for me after, I’m worried I could get jealous, etc.

So for any couples out there (lesbian, gay, straight, or otherwise), what was it like having a threesome and what was the aftermath like? Did it positively affect the relationship? Did it negatively affect the relationship? What was something y’all struggled with (if you did)? Any advice is welcome.