I don't know what others have said, so I may be repeating or I may not. In any case, if there is a repeat then at least you know that more than one person thinks it. If not I hope this perspective is helpful. Obviously you can take it or leave it. In any case this will be a bit of an ass kicking
It sounds to me like its time to put your foot down. You love your wife, I get that, but you aren't setting boundaries and aren't doing what you need to do for you and your child.
I think buddy has to move out first off. Why he moved in in the first place is beyond me. He never should of. There is far too much going on in your relationship to justify it being a good idea. I think it needs to be known that he has to pack his bags and find a place because your marriage is crumbling around you.
That isn't good for you or your child I don't think. Your child will get attached to someone prematurely and that isn't fair. Yours is a tenous situaion at best and they might be eventually abandoned by this person and their mother in a split up that was brought on by his moving in. Why would you want that on your shoulders.
The trip you took sounds lovely for them and crap for you. Why would you agree to that, seriously?! To play the martyr or to make her happy? Either way you lucked out while they had a good time at your expense. Stop doing that. It isn't serving anyone. The balance is off and is slowly getting worse because you don't put your foot down. They are using you.
Its awesome she has two guys but it isn't a competition. She is telling you shit that is making you feel that way and you are allowoing it or asking for it. What they do is their business and up to them. I don't advise you ask about it, involve yourself in it or think about it. That way you can concentrate on what you have with her rather than what they are doing.
It sounds to me like some order needs to happen. Regular date nights where he baysits and you two go out, regular family time just the three of you (child included), regular date nights for them and a complete balance of time. If you all live together then in my experience it works better to be sure time is divided in such a way that EVERYONE is content.
Time to start talking. Figure out what your boundaries are and stick to them when you talk to them. Then they get to say what theirs are and so negotiating begins. Add to them things you want to do; the job you dropped, take it up again, the military, join again, the projects you want to do, do them. I think he should go, but if he stays its time to arrange child care. Organize when he looks after the kid so that you can do some stuff you want. You playing babysitter all the time is not okay I don't think. Again, using you.
Dropping your life to please her is not a great idea. Do you see that? It never was. I don't think you get to play martyr for decisions like quiting because she said. All those things made you interesting and you and now she says you're boring? You have allowed her to create a man out of you when that was your job. You are your own person, love aside, you should be doing what YOU want and need while considering her and your child, not giving up because she said. Start living like that! Maybe she will find you interesting again because of it. I hate when women do that shit, men let them and then no one wins and the relationship ends.
Lastly, I think it might be wise to figure out if buddy is a cowboy. Is he in this to steel her away? Some of what you said about him indicates it might be so.
Straighten up, get your head on straight, think clearly and put your "falling in love with her ten times a day" or whatever aside. I think your vision on this has been severly blurry.