The questions might be better raised in Poly Relationships Corner section. So this might be moved their (or you might want to re post there).
Too not jealous here, to totally come from your husband's standpoint but can begin to...
Relationships are a compromise, so both sides will often have to give up something, though if one side is always giving up everything, that points to an unhealthy relationship.
Question why you don't want to 'have to share' the woman you meet... would you Object to sharing (if it felt right), and/or would you object to him finding another woman?
Try to talk to him again about what You want... and what he wants...
Would you be open, would he find also acceptable..
You can find a woman you have your emotional bound with, that is not necessarily with 'him' also (though you both might enjoy leave it open to if we can 'seduce' the two of you...); however in return if we is wanting a threesome, would you be open to him possibly finding (an)other woman, and possibly engaging in a threesome (you have implied that you have in the past just hooked up to sex, so presumably you can enjoy more casual encounters).
Knowing that you are willing to consider what he wants, but you also want what you need, fulfilled might help him work towards a compromise you both feel comfortable with.
In short you may or may not reach a compromise you both can live with (hopefully you can), but the best advice is both of you need to try to talk honestly about what you both want/need, and try to reach a compromise that both can feel is fair, and gives you what you both need.
Communication and honesty really is the key to relationships that last