Originally Posted by opalescent
Some people are just not poly. They just aren't and that is perfectly fine. You may be one of those folks.
And some are uncomfortable to combine a relationship style as alien to their own as poly can be for a mono person with the one that feels natural for them. If this is the case, the two possible partners are just uncomfortable with each other and things won't work out. But even out of those who are (like Opalscent pointed out) mono and stay that way (out of choice or nature, all arguable ...) there are some, who are honestly and perfectly fine with a poly person by their side. I couldn't imagine that as well when I started 'the poly journey' myself, but both of my men are like this. There will never be a relationship without hardship, that is a given in every last one out there, but there are as many fulfilling poly relationships as monos.
The only things you can do now, is try to basically identify what your deal in this situation will be. Do you want to and (more importantly) can you live like that? This isn't about him 'cheating' you into it, try to put this aside. Before anything else ask yourself the simple question if this would ever be thinkable for yourself. If you want to stay with him, if your feelings/ your relationship is strong enough to endure some difficulties (different ones a mono relationship may have had in stall for you) from time to time. To get a grip on anything there, make this about you, not him right from the starting point.
This doesn't have to be about drama all the time, it won't be roses all the way as well. And you absolutely right, if you have problems in your current relationship, poly isn't for him or both of you right now. The saying 'relationship broken, add more people' is a recipe for disaster. Your gut feeling is absolutely right, don't dive in there on the spur of the moment. Make sure that you come from a safe place and have something you can turn to when things are rough. I doubt that we (husband and I) would have been able to open our relationship in the first place if the foundation wouldn't have been rock solid.
And yeah, concerning the point of view my two mono men would voice if asked: I think I can second everything Questioning has said. But if there are specific aspects you are interested in or problems you would like to discuss with some like minded people in a similar spot to yours, just ask.
Mono/poly is possible but not for everyone. Just like taste or any kind of orientation you can think of. Find out what it is like for you. Good luck.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.