Is it alright that I’m not comfortable with my partners dating specific people? I told my partner that I was not comfortable with it and they were fine with that, but the person interested in dating them has recently started throwing a tantrum about how they’ve never wanted anything more than to date my partner and it is making me feel like some kind of mustache-twisting villain.
It’s alright if it works for you and your partner. Some people in poly relationships find that it works well to give their partners ‘veto power’ over people they date - and if someone makes you feel unsafe, has a history of abuse, won’t adhere to safe sex standards, etc. - then you have very solid ground for saying that you’d prefer not to date someone who’s dating that person.
For other people, it does not work to have their partner approve of or screen or have any kind of input on new partners. I can’t tell you what’s universally okay - I can just say that if it works for you, it works for you. It sounds like your partner is okay with not dating this person for your sake, so between the two of you, things seem fine.
If this person is throwing a tantrum over this, it seems like maybe you were onto something when you felt like they weren’t someone you wanted to be involved in a poly network with. They’re showing themselves to be immature and manipulative, so take solace in being proven right. And if they are making you feel guilty, try to let that go. You don’t owe it to people to give them what they want. You did right by yourself and by your partner. You are not a villain.
Your partner is choosing not to date this person based on your input. It’s your right to give that input and it’s their right to act on it. This person needs to recognize and accept the agency of all people involved. Sometimes we want things that we don’t get. Sometimes we want to date people who don’t want to date us. Sometimes we don’t like their reasons. Being a healthy, mature person means learning how to handle those situations with grace and respect. If someone can’t or won’t behave that way, that’s their problem, not yours.