I'm sorry you struggle with this.
Coming on too strong/too fast could sometimes be a warning sign that the person is not healthy. Was it "love bombing" you to access you for supply, and then when it wasn't feeding his need he cools off seeking other supply elsewhere? But keeps you on the string?
To me it sounds better to let this one go and be rid of all the UGH.
Start over, more slowly.
Be clear on what type on open model relationship it is you want to practice with your current partner. Understand the pros/cons of each.
Going in wanting casual, polysexual fun can sometimes lead to emotional attachment because sharing sex triggers all the brain cascade of feel-good-hormones. Rush too fast into dating and/or sharing sex without giving yourself time to assess a person's character? You could be at risk for dings. If what you are after is "open relationship, sex and fun" and he's offering you effusive over the top love stuff? Could end it sooner.
"Thanks! I'm sorry, that's not what I'm looking for at this time." Shop at the right store.
Do yourself care, give yourself time to heal, and with your next openings go a little slower. Read more, prepare more. That would be my suggestion.
are some places to begin exploring that could help some.