So ive been in open poly relationships before and am very sex positive. The problem is several fold and it mostly comes down to education of everyone involved and comfort of all parties.

1. There needs to be solid trust and communication between all members. If you dont have this it will fail. This is why going open will never fix a broken relationship.
2. Some people arent able to let go of the jealous feeling of their partner being with someone else and thats ok it just means being poly / open isnt for them.
3. Everyone has to be ok with the arrangement before it happens. None of this “I get to kiss/fuck whoever I want but you dont” stuff.
4. The reason you want to be open matters. Do you just find it exciting? Does your partner? Are you long distance and so want to keep your options open? Does the partner know that? Are you into a kink your partner isnt into and they are ok with you experimenting? Are you in love with multiple people and want them all and they are also cool with that? Giant cuddle puddle sounds great? It all comes down to trust again. It can NEVER be because you’re trying to compensate for something your partner lacks without the consent of the partner

If there are any hard feelings in the relationship they will be compounded. So make sure the relationship is solid first.

Also being open doesnt automatically mean each person can do whatever they want. Talk yo your partner about partners you want to being in. Talk to the new people about your current partner. Make sure everyone is kosher about what’s happening (and also make sure everyone is regularly getting tested for STDs)