My girlfriend and I have been together roughly 4 years. Over the past two I'll admit I've been a bit complacent, i want really putting in show effort i probably showed have. Took our relationship for granted. Recently over the past year our sex life nose dived from probably once or twice a week to once a month to not at all. Granted a lot of that was caused by her depression which was exacerbated by hormonal birth control she was on. So seeking to alleviate that we took out the implant and she decided she was comfortable with getting an IUD instead and seeing if that worked. Immediately after having it put in, within a day or two, if I touched her she felt genuinely disgusted. Like a close friend was getting too handsy. She completely lost all sexual attraction to me and even hated being around me. Just looking at me or talking to me put her in a shitty mood. Within a week we took the IUD out and while there was not immediate improvement she now enjoys being around me but not be touched. I also have my reasons to believe she doesn't love me as much as she once did and is considering a breakup.
It's all just happening very fast. Her sister and I are working on compiling ways I could improve on our relationship. We've compiled date and gift ideas as well as a flowchart for how to construct a date as a surprise without giving her anxiety (what info to give her what not etc etc). I'm regularly visiting the gym mainly to blow of steam but also in hopes that I could be a bit more sexually attractive to her idk. My girlfriend and I have also talked about maybe doing couples therapy. She wants to make it work but she sometimes seems like she's gauging how I would react if we did break up. At this point I don't know what to do, I'm terrified of losing but I feel like everything I'm doing is way too much way too late.
As someone that was in a relatively sex less relationship, stop focusing on sex. There's like...a lot more to relationships than your first paragraph. And if all the stuff you mention on your second paragraph is to get to the first, then just give up now. The strength of a relationship is not how much sex you have. A relationship is determined by how much you love the other person and, crucially, that they perceive your love at that magnitude. (It's also determined by extraneous stuff like stress....so look out for that....)
And yes, I did learn this the hard way. I was in a relatively sexless marriage for a few years. Now, it's not sexless in any meaningful way. The difference was mostly her getting off birth control, but also me wanting her to know that I love her so freaking much. And a well-timed back rub without the expectation of sex can go much further than the strongest thrust of pelvis.
Maybe she's changed, especially with hormones it can help her realize another perspective that might fit her more comfortably. All you can do is just try n make her happy, so just identify what does that now and do your best to maximize it (which might even include just giving her space)
Trying to force anything is just going to solidify its place as a negative thing