Thanks again for all the replies. Yes, it'll definitely be a good idea to speak with a lawyer I think to get everything in place. I"m just really happy to hear that it is in fact possible, with the right steps taken, to protect my money if it went in as a down payment. From speaking it her, it seemed like basically if I put it down, he's entitled to half and there's no way around it.
All of this would be for a future home down the line though; it's him who's set on buying right now and I told him I didn't feel comfortable at this point getting into any mortgage together (I want to wait until we're at least engaged), so we said I would rent from him for the time being... definitely a better in my mind. But I think I convinced him last night renting is the better route to go for now anyway as he's really not going to get what he wants with the down payment he has saved up.
This way we can rent, and if engagement does come (I could see it coming in the next 6-12 months), then we can look at buying a bigger and nicer house together and I'll put in my downpayment.
Thanks also for the link to the laws... I'll check that out. I think I need to do a bit more reading on everything to really get an idea of what's all involved. I know I want to start investing my money more, it's just figuring out the best way for me to do so.