Your issue is wirh G, not L.
If you want time with him that is uninterrupted, then it is up to him to ensure that time is uninterrupted. Whether that means he steps up and makes sure she has everything she needs, or making arrangements so that L can get what she needs without relying on G. If she continues to interrupt your time with G, your issue is still with G. It is up to G to figure out how to provide you with uninterrupted time together, if that's what is important to you. You don't have to get into why you think she is interrupting your time together because as far as you're concerned, it's irrelevant. It's not your issue, it's theirs.
If you're not enjoying your time with L, you need to talk to her directly. There's no reason to bring G into the middle. If you can't come to an agreement to be nice to each other, then don't spend time with her.
Me: 48 - Married, straight, male
Shiela: My wife.
Suzanne: My FWB
Adam: Shiela's LDR