In Japanese, how is past distinguished from future?

[Matt]

From what I have learnt, there are 2 tenses in Japanese, and these are past (the english past) and non-past (both the english future and present). How would I say I loved somebody, and how do I say I love someone and will love someone

[askawow 47]

I loved jane
watashi wa jane wo aishite ita
I love jane
watashi wa jane wo aishite iru
I will love jane
watashi wa jane wo aisuru darou

you need to conjugate verb 'aisuru'


ex.
verb 'eat'
-i ate apple.
watashi wa ringo wo tabeta.
-i eat apple.
watashi wa ringo wo taberu.
-i will eat apple.
watashi wa ringo wo taberu tsumori de aru.

verb 'write'
-i wrote letter.
watashi wa tegami wo kaita
-i write letter.
watashi wa tegami wo kaku
-i will write letter.
watashi wa tegami wo kaku deshou

will = darou, tsumori de aru, deshou... etc.

[Jdiesel]

I loved somebody.
Watashi wa ano hito o aishiteta.

I love someone and will love someone.
Watashi wa ano hito o ima mo imakala mo zuto aisu.

ano hito=that person, somebody
imakala=from now on
aishiteta=loved
aisu=will love

[Miyano-sama]

I loved X = X ga suki deshita / X wo shitte ita
I love X = X ga suki desu / X wo shitte iru

Since love is a unintentional feeling, I can't think of a situation in which I would say "I will love someone". But anyway, there are many expressions and grammar points that helps you decided the tense. For example, "ikimasu" means "I go" or "I will go", if use the word "mainichi" meaning "everyday", it will becomes clear that the intend meaning is present:

watashi wa mainichi gakkou e ikimasu
I go to school everyday.

If you use an adverb showing future, the meaning becomes future:
watashi wa ashita gakkou e ikimasu
I will go to school tomorrow

In addition to past and non-past tense, there are also resultative action and present progressive tense. To say that you are doing something right now: use te-form + imasu

watashi wa ima asa gohan wo tabete imasu
I am eating breakfast now

Te-form + imasu is also used for describing resultative action:
watashi wa aoi shatsu o kite imasu
I am wearing a blue shirt.
In the last sentence, you are not saying that you are in progress of wearing blue shirt, but rather you have already worn it. A similar example is:
kare wa kekkon shite imasu
He is married.

Moreover, the word "zutto" is useful in saying present perfect tense:
watashi wa (anata to atta toki kara) zutto ai shite imashita
I've been loving you (ever since I saw you)