Oh yes definitely.
Even if l don't feel comfortable telling him , and l don't think he will understand what I'm going through and slow down my recovery
That someone wants you both to get married you said. Do you also want to get married? If you do, yes you must share with them. Do not fear the consequences of sharing about your ocd (assuming you two love each other). They will eventually find out into the marriage anyways, best to just share it now rather than later. Understanding may not happen over night, but hey at least you're not carrying around the burden of not sharing with them. If there's love, understanding will come.
That sounds like a tough situation, so maybe you could find a way to explain to him what you’re going through and what you need. Maybe also give him some time to process everything. This is something you and he definitely need to be on the same page about.
Yes, I think it would be best to!
I think it’s a personal choice.
I think you first have to ask yourself how YOU truly feel. If you love this person and want to spend the rest of your life with them and you trust them and they are a safe person (assuming they are if you want to marry them), then yes - part of being in a relationship is being real and vulnerable. But if you don’t feel the same way about them or you aren’t necessarily ready to commit to that level yet, I think you are allowed to set emotional boundaries and tell them when and if you are ready to make that commitment. Also - you don’t have to divulge everything at once. If you’re unsure how he will react or afraid he’ll slow down your recovery, then you could start by asking him questions like “how would you feel if I had a mental illness?” Or whatever you were comfortable with asking. See how he reacts and if he is understanding, keep going. That does sound hard though - and that is just my opinion - I hope it goes well whatever you decide to do!