Personally, it took me ages to figure out how to get married, especially without any obvious way to know how to do so, so here is a guide on how to do just that.
How to get married
Secondly, increase your friendship level with them, talk to them everyday, give them 2 gifts a week (loved gifts are better but anything works), and upload a photo with them once a week to do this as fast as possible.
Once they reach 5 hearts, you will be able to flirt with them, this can be accomplished by talking to them over and over until a flirt option appears. They won’t instantly be attracted to you, but once you reach 6 hearts, you will be dating and have the option of kissing them instead of talking, which has the same impact on heart level.
Once you are dating, its time to get them to move in! Go to city hall and purchase a set of duplicate house keys for $100. Then gift this to your partner and they will move in the next day. You can gift them the duplicate house keys even if you have already gifted them twice that week.
Now the last step, getting married. You won’t be able to completely reach 7 hearts until married, but you can still max out the heart before which you must do before getting married. Then go to the VIP area in Gianni’s store and you will be able to find an engagement ring for $2000 on the table Lucy stands at. Buy this and gift it to your partner the same way as the house keys and if you have maxed the hearts as much as possible, they will accept! You will then have a cut scene getting married and the time of day will progress.
Congratulations, you’re married now! I hope this guide helped!
Side note: even after dating or getting married, it says your partners status is still single on the contacts app so just ignore that.