I like you have had similar experience, of sleeping with women that i have known over the years, before and after they have had children(to different fathers though...not myself!)
And i can appreciate your story, and i am sad for you because obviously you are very close to your girlfriend, and want things to stay the same. For me i at least did not have the same emotional attachment, so it wasn't quite as upsetting. However my stupid ego can be incredibly fragile at times, so it still got to me as well! Despite my freedom from commitment.
You should know for one...that there is nothing your dick or a dildo(unless it has crazy vibration) can do that your hands can't, in terms of stimulation.
I have given multiple girls earth shattering orgasms from going 4 fingers and beyond, with foreplay. A bold statement..but i'm a modest guy (i've given some utterly awful sex in my time too lol) But, Soaked sheets, and convulsion-like shudders don't lie , so i have the validity there for you to trust.
Due to my own multiple experiences...To this day, no matter what gains i make with PMMA, i know that no matter what, our hands...mechanically...and in terms of raw stimulation, void of psychological factors... will inevitably always deliver more than my own...or anyone elses cock. They are firmer, larger...easier to control...and you can angle them however you want.
And in cases where girls have had kids, they are a lot more capable with the 'space' provided.
^^^ so keep all that in mind before feeling like you're now rendered worthless. Because you really arent. I even got invited back by a girl who i couldn't even get hard for, because i drank my dick into a limp vodka induced flaccid coma. Simply because my hands bought the A game with them. (my point being with all that - you can still drive her wild with your own flesh rather than plastic, dont worry).
Of course though i completely understand that its never quite the same as pleasuring someone with your own dick. Its much better when it is mutual for sure. I'm still the same...why else would i have opted to undertake PMMA myself? Also of course theres a lot more psychological aid with stimulation for both yourself and your partner when you are using your penis instead of your hands. She'll instinctively be more turned on because she knows you're enjoying yourself too etc. So of course its still very important.
From experience of years of clamping, pumping etc etc....i would not recommend that you go down the air pumping route. I can tell you by comparison, that i was able to pump my 5.4 inch girth right up to around 7 sometimes....and it'd look monstrous...but its all just edema under the skin...soft and squidgy..no real firmness. Its a very superficial gain. Not to mention the time it takes in the pump to achieve this can be quite damaging to your nerves, and blood vessels, especially if you make a regular thing out of it. To gain up to an inch of girth in a pump,
I know so many air pumpers who have given themselves poor erectile quality or just full on ED. Also you'll probably have to have the thing on for a good 30mins before having sex. Which could be massively inconvenient for you and your girlfriend.
I am at the beginning of my PMMA journey, so i cant speak for the future, some people on this forum have been through hell and back so its important you read as much as you can before you weigh up what you wish to do, but with my current results, even with imperfections, and nodules at my injection sites..... i *personally* would still go back in time, and do PMMA, instead of all the years of dick torture i put myself through, trying to enlarge it through natural means. I gained 0.5girth from it all (clamping and edging mostly), but it took ridiculous amount of time, privacy...a lot of pain, and realistically has cost me a fair loss in sensitivity...and hanging did nothing more than loosen my skin.
But i am speaking for myself, some guys have really fleixble and weak tunicas and can gain more effectively without having to be so tough on their dicks. Mine unfortunately was cast iron when it came to length. And soon became that way for girth after gaining 0.5.
If you insist on trying a pump at all, i'd recommend using bathmate which is a water pump, for some reason water vacuums are not so harsh on the blood vessels, and are more secure. Plus the warm water helps your dick to relax much more and expand with greater ease. You'll also soak up some of the water, giving you a heavier more solid sense of fullness. But it still wont hit the walls of your gf's vagina like solid PMMA.
Good luck finding what is best for yourself buddy, I hope whatever approach you take resolves your issues.
For now whilst you dwell on what to do, id say, make the most of your hands, and alternate them with penetration, that way you are both having fun. It worked well for me.