I get what you're saying, yeah. Truth is, you want them to split, you want him to yourself and, with that in mind, do you honestly think you'd be able to be just friends? My answer is No.
With with honesty in your mind, can I suggest you talk to him and express your honest feelings and what you're thinking and why. You'll unlikely be able to just be his friend since you want more, you really do. He obviously sees the same thing or he wouldn't allow the cuddling, massaging etc to happen in the first place.
He needs to make a choice for the better future of all three of you. It might take time to get there but you guys need to be planning on sorting out the future of all three. If he decides to split with the current GF, fine. If he wants to remain with his current GF, that's got to be fine too. At least you know you need to move onto something else then and a better life.