people have their views and you have to respect them.
How about creating a plan?
say you have 100k together.
What if you divided that by 50% (and put 50k in the bank as a joint account: and then put 25k in a personal account (25k for him to what ever he wants: and you the same).
After all: what is money but paper if you do not do anything with it... ???
At the same time : I am very frugal and very conservative: and I understand his fear of losing it. In this scenario: the majority of the funds (50%) stays in a safe fund (think mutual funds etc) to also make it grow in a safe way.
Now you have 25k (which may not be much now: but from this point forward: maybe 10% or 15% of what you make in real estate sales goes to that fund: until you have enough to invest by yourself. (always making sure he knows - he is invited to join with his personal funds if he chooses): you are a team after all so you don't have to rub it in his face if you prosper. (If you do prosper and are successful, then great and enjoy the money with him there after): if you lose it all together, ahh well, you live and you learn! and you planned for it.
Find something about real estate he likes:
maybe he is methodical and a type S or C personality : so maybe he will want to take part in accounting, managing and other number driven activities:
maybe he is a high 'I" : where he will like to have a say in the interior aesthetic and design or talking and interacting with the tenants etc
Or a high D type: and he will like taking action: negotiating etc (doesn't sound like this one though )
He has to fall under one of these 4: so assess- learn about each other and make it fun.
No one wants to lose their money- of course not: but take action, research and learn: get a mentor or partner already doing it.
I bet you both have jobs and salaries : and can get back up if you do something wrong.
Good luck