In my book, a person's "first experience with ENM" is not when that person has an experience with a new partner, but when that person's partner has an experience with a new partner. If you and your partner are not both completely happy with the other having relationships with other people, you are not suited for an ENM relationship.

Also, it seems like you both only want ENM when it's inconvenient to commit to mono. It doesn't seem like either one of you would start fresh and choose only ENM relationships for yourself.

Frankly, I think you should live separately until your relationship is sorted out. When you can each go a full year or more perfectly comfortable with your partner's freedom to pursue other sexual and romantic relationships, then you should maybe think about long term commitment and what you want it to look like.