@Abigail May,
You need to want this and be comfortable with it.
Do Not Do this for your boyfriend unless your completely comfortable with it.
There will be some first time jitters but they usually go away in a short time.
Discuss this with him and set rules on what will be allowed to happen and what won't be acceptable. Have a 'safe word' that means everything will stop and no body takes offense to stopping. EVERYONE must respect this stop request, no matter who calls stop!
Also consider what is to come next or what will everyone feel after the first time.
From personal experience, our first MFM led to more outside partners in several different experiences. For both my wife and myself, we had thirty years of wonderful experiences but it is not for everyone!! We were three years discussing the first time until we were both comfortable with doing it. Go slow as many relationships do not survive this avenue.