Rules/Restrictions

Me (M25) and my girlfriend (F25) have had more than a few experiences with swinging, mostly just with other girls but occasionally other couples as well. We both have things we’ve agreed on that are dos and don’ts and we seem to agree on most things. One thing that she is highly against (which makes sense and I can understand why) is, she doesn’t want me to finish in another girl. She’s very adamant about making sure that doesn’t happen and although it’s not something I’m upset about not doing, it would be nice to be able to do. Anybody else been in this situation or have specific “no-nos” you have with your S/O?