Stop feeling threatened by your discovery - it is actually a huge opportunity to take your relationship to a new level that few couples generally achieve. You have made a discovery about your partner that a lot of guys make a mess of (well, I did - this advice is from an experience I had with my then partner when was in my early 20's). You've discovered that your partner has a greater sex drive than you were aware of! Your cock is not the total solution to all her needs after all. That can be a crushing blow to a young ego but you need to get over that if you wish to really connect with a woman. The attitude that comes through shows a typical young male full of hormones and a need to dominate and control (which is the core concept to the definition of "ownership"). What do you want - a soulmate or an asset? If it's an asset, well don't bother reading anymore, your future is just going to be a little pinprick in the dark when you could go down another path with your soulmate towards a never ending incandescent adventure.
Don't let on that you know anything about your knowledge of the farm produce - you might be jumping to a false conclusion. Did you actually witness that thing up her pussy or are you making assumptions that she did based on your fantasy mixed with the smell of condoms and lubricant. The condom might have simply been used for hygiene, and lubricants used for external stimulation.
I would suggest that you think about taking advantage of your new intelligence for deeper bonding with her. What about planning an evening out (any excuse for a celebration will do, but no friends) - perhaps a romantic dinner at a restaurant then afterwards visit an adult shop that just happened to be on the way home (if there are any near you that are open late hours and go in, encourage her to try a few things on (lingerie, knickers, bodices etc.), show her a few toys (vibrators, dildos, and DVD's). Alternatively, just happen to go online at home with a glass of wine at hand and accidentally find an adult website that you accidentally found by typing error. Order something from the myriad number of retailers and warehouses that specialise in adult products. These are usually about a third of retail prices and just waiting for the arrival of your parcels engenders a horny mood in anticipation of playtime.
Also, while you are in the planning phase, go online and google "Tantric massage" have a look at some of the training vid's (Youtube) available. Also have a look at some of the other massage techniques (Japanese looks fun and a good full body precursor to the main event of tantric massage) and how to make her yoni happy. Importantly, you must be patient - a good full body massage (not deep muscle, just a methodical rubdown in a certain progression) can take between 1-2 hours, half an hour for the tantric. Again it depends on the girl too. These times are expectations for an ice queen, but it doesn't sound like that in your case.
Learn the basics and you can ignore all the spam and advertising crap on the internet offering to teach you how to make your girlfriend squirt and adore you forever (for a ridiculous fee).
You will find all types of people on this planet, each with similar core "survival" instincts - ie. sex - the urge to reproduce the species; yet each individual has different levels of drive and preferences. Some women can match the male with high levels of desire, but few respond to visual stimulation the way men do. But if (as your lady seems to) likes to masturbate and uses a cucumber, then what's wrong you taking her on a new path where you can participate in the play as well. You can have a wonderful afternoon just sitting on the lounge watching your favorite movies and mutually masturbating each other as foreplay before the best sex you have probably had.
Get rid of the preconceptions you seem to have about women and their sexuality - they are more varied than you can imagine. If you really want a long term relationship with her, then start treating her intelligently and imaginatively. Let her know she can confide her deepest dirtiest secrets and fantasies with you and that they will be safe in your keeping (ie. don't go bragging to your mates). Then start thinking about your own sexuality, return her confidences and let her know of your deepest dirtiest secrets and fantasies and you could be looking at a never ending honeymoon.
Good luck