I'm sorry to hear you're going through a difficult time, but I'm happy to see that you have a partner who's very patient and receptive to you. As someone who got diagnosed with severe OCD late last year and had my relationship go through essentially a breakup in part because of it I don't know if I'm the best source of help, but I'll do what I can.
I think something that helped me a lot with dealing with my OCD regardless of the status of my relationship is being able to stop and take time to face OCD. What I mean by that is that OCD I think of as a bully when you don't entertain OCD you rob it of its power. It's funny because a minute before I found your post I actually had to take a moment to collect myself from a mild OCD induced anxiety attack. This may sound like a paradox though, right? How does one both face something but also not entertain it? The answer to that at least for me has been to sit with myself to lay out that the irrational fears that OCD is presenting me are just that. For example, it could be something like my partner COULD be cheating on me BUT they also might not be.
This in and of itself is an exercise that involves you interacting with OCD, but the funny thing is when you're able to do that instead of running to compulsions what you'll find is that you are weakening OCD every time. It's kind of like when you go to the gym and lift weights. You break down your muscles only to get stronger so that the thing that was once so heavy eventually becomes light.
I think if you're able to practice that when you notice these thoughts coming it'll be very difficult, you'll probably feel an anxiety at times, that's a 10 out of 10, but if you keep working at it, it'll go lower and lower.
The good thing is is you have a partner that is already aware of what you have and so if you're able to just convey that process and so he can understand what you're doing that can also help. One thing I will say is that compulsions, like continuously explaining to your partner what you have for reassurance, is something that you have to be careful with. The reason why I say this is because in moderation an action like communicating to your partner is not inherently bad at all obviously, but depending on the context it can be. How can you tell when an action is a compulsion? Here's how I did it and it's with one simple question you ask yourself:
Am I doing this action out of fear first and foremost? If the answer is yes then that's when you practice sitting with yourself, even if it's for 5 minutes, in silence and you notice the thoughts that are coming and going. Y let them flow through you but don't entertain them or go out of your way to silence them.
The thing with OCD is it's all about learning how to be okay with being afraid, not eliminating fear. OCD wants you to think we have to always run away from our negative emotions when in reality it's a trap so that it can do exactly that, keep us in a endless loop of negative emotions.
The last thing I'll say is that you have to be able to be patient and forgive yourself. I've learned that forgiveness with yourself isn't like forgiveness with another person. Forgiving yourself is an ongoing process while with someone else. It kind of climaxes in a moment. Unlike with another person, you never truly get to have a closure moment with yourself because the actions you did are in the past just like how you can't get closure from a person who has passed. So instead what you do is everyday you work on yourself to change for the better. With every day, every week, every month, every year, and so on you'll slowly change more and more and at some point you'll wake up and you'll realize you're a lot better than the person you once were. That the OCD and the emotions that once claimed you so strongly don't do so as much anymore.
In short, my advice is to practice facing OCD instead of running from it, be aware of compulsions that would feed your OCD by asking yourself are you doing things out of fear and if so wait a moment to calm yourself before doing anything, and lastly learn to forgive yourself which is an ongoing process and not something that happens in a single moment. At least not when dealing with yourself.
I hope this helps. If there's anything else I can give clarity on I'm more than happy to. Regardless though you got this and if anything I said spoke out to you please let me know!