I have been in a very happy relationship with a married couple for a few months now, and we all love each other quite a bit.
I have express my wanting to have alone time with just my boyfriend, and my girlfriend has said it’s ok many times, but afterwards tells me how much it hurts her, which makes me feel extremely guilty.
And now I’m beginning to resent her because she’s basically completely in control of when I can and cannot have sex
I’m beginning to not have any attraction to her, and am constantly living in fear that she is going to say “no more this is over”, then I will lose both of them, but most importantly my boyfriend who I am madly in love with.
Am I not being empathetic enough to my gf?
Are there any other thirds here who have experienced this and can give me any tome of support and advice?
We see this situation a lot with triads, especially the kind that involve someone joining an established couple and trying to date both of them. It's extremely difficult, if not completely unrealistic, to expect that the feelings and dynamics between all three dyads involved will always be exactly equal.
In fact, I wouldn't even consider a relationship a true "triad" where there is talk of "secondary" partners, or labelling of the non-married person as their "third". This smacks of couple privilege and the dreaded "unicorn" syndrome.
If the married couple/established couple get to call all the shots - or the wife in this case tries to control every interaction between you and "her" husband - how is this loving or fair to you? It seems pretty clear to me that she feels threatened by any time you spend with her husband by yourselves... which probably stems from
a fear that:
a.) he may leave her for you one day (insecurity)
b.) he prefer your company/think you're better in bed/more attractive (jealousy)
c.) she is being left out, ignored, when you're not all together (envy)
If the husband (your boyfriend) doesn't stick up for your/his right to participate in a romantic dyad of your own, and doesn't desire/suggest/insist on being able to have alone time with you, himself, then he's not being a very supportive partner
to you.
If this is the case (not saying it IS), your boyfriend may believe he IS supporting
his wife by not being too forceful in this area... which in turn makes it seem like you are the one coming between them, AND reinforces the notion of couple privilege (he puts her feelings first).
To play devil's advocate on behalf of the wife, however...
There are a number of statements you've made in your OP (in bold type) that lead me to believe that things aren't exactly on an equal footing insofar as YOUR feelings for this couple you're dating.
1.) you say you love them both "quite a bit", but only describe your feelings for boyfriend as being "madly in love".
2.) you only talk about wanting "alone time"/sex with boyfriend... but don't say if you ever ask for/want/have time alone with just your girlfriend, in order to share sex and intimacy.
3.) you describe the wife as feeling jealous, hurt and trying to control the time you spend alone with boyfriend, but don't say how your boyfriend feels about you and his wife dating or being together sexually, without him (if that ever happens).
In other words,
your main romantic and sexual focus appears to be on your boyfriend in this scenario. Since you're supposed to be dating BOTH of them (and they you = triad) this dynamic seems somewhat skewed in favour of boyfriend/husband.
If that is the case, it'd be pretty natural for wife/girlfriend to pick up on the fact that you care more for your boyfriend than you do for her... which in turn is probably the source of much of her insecurity. You don't actually say in your OP if you're "in love" with your girlfriend, or she with you. Are you? What is THAT relationship like, when husband/bf is out of the picture? Can you work on making it more solid?
If not... and you really DO have much stronger feelings for your boyfriend than his wife/gf... it may be kinder all round to end the relationship with her, and transition this "triad" to something more akin to a "Vee". (You don't say if you all live together.)