I’m in a mono relationship, but I want to try opening it up a bit, and maybe experience polyamory. How should I bring up this topic with my partner? we’ve talked about an open relationship if we were forced into long distance, but never in our current situation. I’m just nervous because they are sometimes insecure and jealous, and I don’t want to trigger that reaction.

The way to start the conversation about polyamory takes pretty much the same skills as actually being polyamorous. Be patient and go slow, giving both of you time to adjust to new terms and feelings. Allow for and expect things to change. Be completely open and honest with each other. Don’t use pressure, ultimatums, threats or other forms of manipulation, and never put up with them from your partner. Take a deep breath, smile, and start that conversation in an unthreatening tone.

The fact that you’ve talked about it already gives you a great way to start the conversation. Say, “hey, remember that thing we talked about doing if we were ever long-distance? I’ve been thinking about it, and I think that might also work for us even though we’re still living near each other. What were your thoughts on polyamory when we talked about it before, and what do you think would change if it wasn’t long-distance?" 

But I need to end with a note of caution. Some of the language in your question throws up little red flags. Jealousy is a natural part of relationships, but that should be treated like a weed to be uprooted from a garden - not a character trait taken for granted and worked around. That your partner can be "insecure and jealous” is a problem you two should deal with even if you don’t decide to go poly.  It’s not your job to tiptoe around your partner’s insecurity. You should never feel “nervous to trigger a reaction” in your partner, not ever. Relationships should not feel like loaded guns. If your partner responds to anything you do or say - especially if it’s just you honestly expressing your feelings and needs - in a way that makes you feel threatened or upset, that’s not healthy, and not something you should put up with, whether you’re mono or not.