So many elements of your story sound like what we went through not long ago...
We had hoped our "M" was just not mature enough or not ready, but the fact is, if she can't live this life now, she will never be able to. Some people have a need for that "normal" life & we can not rob someone of a normal life.
But by all means, don't give up if its not time to give up, just keep in mind there are penalties for living a "non normal" life, but the rewards are FAR greater than any penalty.
This link has some good points & we found it VERY helpful
As for the jealousy, it is GOING to happen, because emotions are not rational, even I got jealous of Heather & M when they spent time together, but the test is, can you (all ppl involved) get past it & use it to make the triangle stronger. And if the relationship is already having trouble before you joined it's not a good sign. The stronger & more stable the couple is, the stronger the triangle will be.
In reply to your question, I don't know, we didn't really try to make it a V because she left, but I can't imagine it being at all easy, feelings like that don't go away quickly or easily, not that you would want them to.
The key is going to be communication, when people stop talking hurt builds up until something bad happens.
We are still figuring some of it out as we go along, but you can talk to Heather & I if you need any help or have any questions :-)