As for the guilt, it's how you feel; if you feel guilty, even if I rationalize that you are not, you still feel guilty, and the guilt will affect you. Vice versa.

Why do you need to define your relationship? Perhaps there's no definition you can find to fit it; perhaps you just create one.

What you need to do is to find the best way to avoid harm.

If you two decided to keep both of your families intact, then please, don't go further. If you are happy now, then keep the way as is, but don't go further. If you are already happy, please don't go further to be happier.

The toughest part of feeling is that it's uncontrollable when it exceeds limits. Please don't go further when it's still under control.

Love is a feeling that human creates. It brings happiness when it doesn't interfere with normal life. It's just one of the finest art and enjoyment. Just like any other interest, please don't overdo it. Once it's overplayed, it will hurt you. Please limit the frequency of your contact. It should be the last task you think about if it will be the first entertainment you go for. Regard each other as a sincere friend.

If you go further till the feeling outweighs the mind, my advice will be redundant.