One has to be very cautious with the whole mates and relationships thing.
First off, you've got to remember to try not to take an ingame relationship too seriously, whether it be just for roleplay or an actual relationship. In roleplay, it is just roleplay - try not to let your thought divert away from that concept. As for actual relationships...well each to their own. I personally am not a fan of online/long distance relationships. I had a friend who came very close to this lad she met, who just so happened to be on the other side of the country. The location situation could have been worse, but because of the age they were at, they couldn't exactly get on a train and see each other. So, in the end, it didn't work out. Plus, how well do you really know that person? Perhaps everything they tell you is all lies so that you will like them. Don't trust anyone completely. It's better to be suspiscious and safe, rather than sorry.
I have no problem with people having 'mates' in-game for whatever reason, providing they are responsible enough to take care of themselves, like not letting themselves get too carried away, or drawn into doing the wrong thing.
If you're going to have a mate, know that there are things that you should and shouldn't do:-
Cuddling up is fine
Just talking as mates do - completely fine
Depending on the maturity level of both individuals, mature conversations really must be done in private, please
Doing inappropriate things is certainly not fine
Unless you are completely sure that you can trust them, don't give out personal info e.g. address, phone number etc. If you do, you do so at your own risk. You have only yourself to blame if that person turns out to be a perverted stalker.
As for whether a person loves the character or the user behind the character...I think both can happen. In a roleplay, characters fancy characters, not users fancy users, unless a couple of users do a lot of OOC chatting. Having a conversation as yourself and not behaving like your character I believe can possibly lead to someone fancing the person rather than the character. It all depends on the situation really.