My GF (24F) is pushing me (25M) to propose, despite relationship struggling

We got together 2.5 years ago, she moved in to my place immediately, because I didn't want her to live with her ex. She is my first gf and instantly became my world. Things were going great to start with.

Sex has been a difficult topic. To cut it short, after first month's we're crazy good between us, I eventuelly couldn't keep up my performance and asked to reduce the amount (not every day, but 3-5 times a week or so). This was barely an option, leading to alot of chaos and disappointment in the relationship. It got to a downwards spiral, where I kept stressing myself heavily about sex thus making it even more difficult. Anyhow, eventuell she told me she lost any interest in having sex and will never regain any interest of it. She "allows" me to have sex with her, but she is holding herself back heavily. She says because after all "this is waht i wanted".

IN MY MIND to solve this issue, i have to prove that i still can deliver. However, truth be. In the long run i will never be able to have as much sex as she desires. So i cannot solve this issue and she will never open up again. Currently, we are at 2 times a week, she prospects it will soon be the last time. Quality also suffers, because of larger breaks I can't last as long as i used to. However its tough for me to initiate more often, when she is not into it

She is callling pur relationship "old people", because lak of sex, and last year after i got a job we have way less time together, so she stsrts to feel everso bored. She is pleased with the rest tho, salary is good and we still love each other after all.

DESPITE that she is pushing me to marriage. She wants to get married at any cost. Be it with me or anybody else(also partly due to her family).

Just one year ago, she almost left me for another guy. Our relationship came on hold for a few months, but we came back together. Since then i get really jealousy increased alot.

I love her, she is my world and i can't be happy without her. She loves me too i believe. But i just know im not her dream man, she is living off compromises, which she accepts to get married. We both are not satisfied with the situation of the relationship, and i never imagined to propose in such situation. But I don't want to lose her, so i am in shambles right now.

There are many more good parts about our relationship, also some more bad parts leaving doubt, but I don't want this to get too long.

Waht would you people do, propose to your love, despite having seemingly unresolvable issues?

TL;DR: Our relationship is struggling, and a big part is sexlife, which declined heavily after the first few months. Despite she wants to marry for the sake of marriage(family reason) but I never imagined to propose when we were both not completely happy with each other. Now I have to propose, in order not to lose her. I still hope to fix things, but marriage is a large bet if we can't figure this out.