Okay, so your friend doesn't like your new partner - here's how to deal
There's nothing like the excitement of a new relationship. It's only natural that you want to spend a lot of time with your new partner, so that you can get to know them really well. You're ~daydreaming~ about them a lot, and you probably talk about them to your friends just as much. Since you think this person is so great, you're sure everyone you know will agree.
Sometimes, that's exactly the way things work out. But sometimes it isn't.
People are different, and not all of us rub each other the right way. Just because you think your new partner is the best person on the planet doesn't mean everyone else in your life will feel the same way. If your new beau treats you poorly or is legitimately a bad person, your friends might have a point, and wouldn't be wrong to try to find a way to help you see the situation for what it really is. But if your SO doesn't fit what a friend thinks you should be dating for other reasons, that's a different situation, one that should be handled carefully to preserve your autonomy along with your friendship. Most of the time, friends should find ways to respect your dating decisions, and be civil even when they don't like them. But not everyone is going to see that right away, so here are a few ways to deal when a friend doesn't like your new partner.
Consider the friend.
Before you do anything else, take a moment to think about the person with the opinion. Is this friend generally wise when it comes to relationships? Does your pal have any knowledge or experience with this person that might influence their opinion? If your friend usually withholds judgment and is pretty smart about relationship matters but still doesn't like your new partner, they might be on to something.
On the other hand, if your friend is quick to pass judgment on others, they might not be the best person to listen to about your love life. Could they be jealous of the time you're spending with your new beau? If your friend has a motive, it might be better to address that concern rather than the relationship with your partner.
Whatever the friend's reason for not liking your new partner, it's important to honor the friendship and respect your friend enough to listen to them explain their feelings, if they want to tell you. While considering the friend's relationship and other life experiences along with potential motives (see above), try not to be quick to react to what your friend has to say. Understand your friend cares about you, whether you agree with them or not, and that's why they feel invested in your dating life.
Be firm, but not dismissive.
Although it's good to listen and respect your friend's opinion, you don't have to follow their advice. You have a right to choose the people you date, and what you want in a relationship may be different from what your friend thinks you should want.
You can thank you friend for caring and for being brave enough to step up and tell you how they feel. You can acknowledge their concerns, and that you value their opinion. You can agree to disagree, but try to be clear on what you expect from your friend moving forward – respect for you and the person you're dating, whether your friend agrees with the relationship or not. Explain to your friend that you hope they can get past their misgivings about your partner and not make your life more difficult than it has to be. (And, once they've told you how they feel, if you don't want to hear them complain about your SO anymore, you have the right to tell them that, too.)
Help them get to know each other.
Sometimes people start off on the wrong foot. Sometimes people make bad first impressions, or even second or third. Sometimes people just need time to get to know each other and find common ground. They could share an obsession for watching The Walking Dead, or maybe they both enjoy cooking. Shared interests discussed when you're all together could help break the ice. Your friend might not have given your new SO a fair chance, and once they have, maybe everyone will be friends. And if not, they can still become amicable. When it's important to you, bring everyone together, but otherwise you may find it best for these people to not spend too much time together.
Remember, you're allowed to date whomever you want, and it's great that your friend cares — that's why you're friends, because you love each other! — but you don't have to agree on everything. If your significant other and friend don't end up becoming friends, the best case scenario would be that your friend will still be courteous to your partner, for the sake of your happiness. Maybe you'll end up together forever or maybe you won't, but your friendship will persevere regardless if you and your friend can remember to love and support each other, even when you disagree.