This situation is pretty hard for both partners. I remember breaking down several times because I just wanted to feel good but it always just hurt. It took a huge toll on my mental health for a while. Most nights sex ended with tears and a panic attack. My husband was my rock through this time period. I know it affected him too, he hated seeing me in pain and he has a super high sex drive. But he never said anything negative, always reassured me we were ok, he was always good with changing up what we were doing to make me more comfortable etc.
It did take a while before we were able to figure out what I needed but we are so happy we stuck with it. I never tried the dilators....just looking at them stressed me out and made things worse for me. I read several comments and immediately knew I needed to speak up. If you've never gone through something, it's impossible to know what it's like and how you would actually respond. I agree with you in asking if people would leave their partner if they couldn't have sex due to chemo etc. That's a pretty crappy thing to do to someone. Vaginismus and pain during sex is a hard thing to go through, especially if you dont have an understanding and caring partner. Lack of sex and sexual frustration can be just as damaging to women as men. This typically isnt talked about so women have no idea what to do. Drs don't even know what to do. Every person is different, so different things work for everyone.
I'm so glad you reached out and want to help your partner! She's lucky to have you! Hopefully you guys can get on the path to a more enjoyable sex life. Once I started enjoying sex and knew my husband was there for me, my libido went through the roof. I could finally have fun and orgasm. You said shes offered blowjobs but you just feel guilty, when she starts to enjoy sex more, that guilt will more than likely fade away as you both will be able to enjoy more things together.
Also, once penetration is starting see if you can find a good position where she is in charge of the depth/speed. Being in control of that in the beginning helped me with avoiding quite a bit of pain. Let her take as much time as she needs to let you inside.
I will leave off on one note that I've mentioned before. This can be a permanent problem that needs to be addressed and reassessed down the line. Something might work for a while and then it doesn't. Something might start working that used to not. Half the time I need naked cuddling, no vaginal touching for a while, touching of other places on my body to get warmed up and it's been this way for years. Half the time now we can have quickies and sessions with minimal foreplay without *as much pain in the beginning. Sex is still painful sometimes but it's to a point where we know how to fix it or if it's bad enough calling it a night. We only have to stop due to pain maybe once every 3-4 weeks now. We both have high libidos now so compared to how often we have sex, that number isnt too bad and I'm happy with it.
Goodluck on your journey! Dont rush the process of figuring it all out. Set aside several hours as often as you can to just naked cuddle, rub each other, experiment with different things/toys/lubes/games and to just talk through it. Communication is said all the time....because it works when both partners are communicating, listening, learning and willing to make changes. We always end our days with talking with one another about anything and everything. We are extremely close and still in "the honeymoon phase" 10 years after marriage and nearly 15 years together. We make us time a priority.