Practice as close to live set up as possible. Familiarity will help you be more comfortable.
If you would prefer to sit down ( try standing up at least and practicing to see if you can get comfortable standing, Arrange for a bar stool so you can sit or stand. Start out sitting as that way you are most comfortable if necessary. The bar stool also gives you a prop, which can be useful for calming nerves etc.
Get some friends around and play to them in your front room, but don't just play, perform.
Relax. Bring the audience into your performance by picking a few people and make and hold eye contact while you play. So get used to playing and not looking at your hands.
Play through the songs in 3 ways:
playing only guitar (get your bf to do the singing)
only singing (rely on your bf to play the guitar to allow you to nail the vocal)
play and sing
Do all sitting, and all standing.
Perform to your bf while he performs the same song to you, together. It's a great way to strengthen your connection with a fellow performer, get synched mood wise etc.
Try to not take comments and crit about your performances seriously. as you progress, or if you are reasonably confident, video your perofmances so you can tighten up how you present your music.
Getting familiar with your audience is a good idea. Talk to them. Have prepared stories behind songs etc. It helps them buy into it and helps you make a connection with them that can ease performance nerves AND make the audience connect to you as a performing artist, and with your songs directly.
Try playing in front of a mirror. Full length if possible. Similar to the video, but more instant.
Remember, it's the song you are trying to deliver well. So when you perform, take a second to get in the emotional state that connects YOU with the song. If you connect with that emotion and get used to it as your performance friend, by being involved with the song, nerves about performance will fade into the background and help you perform better.
Definitely, the more of these warm up performances you do, the more at ease you will be on the night. Every day, even several times a day, is a great idea for confidence building, plus it hones your performance. Much like any practice, it brings familiarity.
I hope these ideas help in some way
Cheers
John