Is it normal to love someone like this?

I've never been able to mix with people and I've recently moved to Spain, meeting people is hard for me anyway so I decided to try Internet dating things were a bit awkward. I got into the hang of it though, I met a few people but it still didnt work out.

I left it for a while, and a few months later after no look in the real world I gave it another go except on a different website. There was a lovely guy on there who was handsome and fitted what I wanted, I sent him a message and we just clicked. There was only one problem and that was he lived far away. We spoke over the phone, email, messages. And things were good. He'd have strange turns though, I won't bother explaining them I'll just say I found out he's mentally ill. It was hard because I am utterly in love with this man, and I will stand by him. But is it normal? He'll completely change some days and I won't know who he is, or he'll not message or reply for weeks but he doesn't mean too.
I'm beginning to feel it's my fault and sometimes I want to walk away but I can't. We are great together when he's on form he's the only person I get on with. And I understand what's going on partly. But I partly blame myself because when he goes away for ages I feel it's me he's getting away from.

We both love each other a lot, but some days it feels like he isn't interested and he doesn't want me anymore.