The world around us is a pretty unstable and unreliable place; circumstances that we took for granted yesterday simply don't hold anymore today, things or conditions we relied on break away, and people may come into our lives and then drop out of them again. While some of these developments can be foreseen, we must expect surprises all the time as well. And in particular when people are involved, these surprises have the potential to hit us heavily. An unexpected encounter with someone for the first time can change much of the world around you (just think of falling in love); but equally can sudden loss of someone whom you loved and met with much affection tear the universe apart.
This sort of risk inheres in any kind of relationship, in fact, in any sort of attitude towards what's outside our own control. And obviously, there is no way of avoiding that risk, short of avoiding attitudes and relationships at all — which would leave us in an impossibly impoverished situation. Taking a stance towards things and circumstances, and getting engaged in relationships with people (on a broad range of types of relationships) is part of what makes us what we are: rational agents, beings capable of thinking about, feeling toward, and acting upon our environments, communicating and interacting in innumerable ways (not least of the affectionate sort) with fellow humans, those who find themselves in that very same condition. If that is what we are, then risk is unalterably built into everything that goes on between ourselves and the world around us. Nothing there is stable or reliable, or if it is, then that is merely relative and tied to some condition; in general, there is no guarantee for anything we may assume. And while we often have to act as if we could take things for granted, while for many stretches of our lives we can more or less safely ignore the pervasive risks inherent in our condition, and while that assumption frequently is even borne out by the events, still we must be clear that sudden loss will come over us, from time to time, with or without warning, and sometimes where it hurts incredibly much.
If risk is what we have to accept, is there anything to be said, or to be done, then? Being aware of it can help you, in at least two ways: you can, in the event of loss, react properly and with strength; and you can prepare yourself (which is something that you can only achieve by constant awareness of the fact, and by moulding your responses deliberately). The latter is, of course, requisite for the former. It's very difficult to respond in a decent way to a great loss if you haven't worked beforehand to facilitate just that kind of response.
The emotion triggered by loss (especially loss of a person we loved) is grief; and compared to many other emotions, it is a very strong and intensely felt one. However, your should be aware that the intensity of your grieving is not a measure for how deep your love was; and neither is its duration in time. I know this may sound cold and cruel, and perhaps you'll find it also counterintuitive. You may think that the depth of your relationship, the strength of your affection, the importance of the lost one, should show itself proportionally in the intensity of the emotions that result from your loss. And conversely, would not a relatively calm and composed emotional condition rather indicate a similarly passionless antecedent attachment?
Tempting as this line of thought may be, it doesn't hold in the face of psychological fact. Scientific studies have shown that most people get over deep loss after a relatively short time. There is variation, but also a discernible mean period after which grief symptoms recede and the impact on feelings cools down substantially. Given the variety in relationship importance, this comparatively invariable resilience seems to suggest that there isn't that much of a correlation after all between how important someone was for you and how long you're entangled in grief.
And if you think about it, why should we assume that an acknowledgment of someone's importance in your life would have to be expressed primarily in an inability? Why should we think that it is appropriate and sensible to no longer think clearly and feel appropriately, to stop and cut back engaging in important projects in our lives — in response to an event that has disrupted us already? Why increase that effect by giving in to its tendency and letting it grow? Any loss will touch us; if we have appropriate feelings towards someone, then we will feel deeply at the sad news that this person is no longer, and that we won't enjoy their presence any more. Still, feeling this and giving way to the emotion are two separate things: we might refuse to be controlled by what is, in the end, a feeling only. And even though it's difficult (quite possibly an almost unreachable ideal, something that only few might attain at all, and something that we possibly can only reach in an imperfect way), is it not important to decisively counteract that feeling in all the places where it doesn't belong? Of course, in a period of grief, after a heavy loss, there are moments when we meditate and perhaps open up ourselves to that feeling of loss. At other times, however, life must continue, and then a proper attitude would rather call for strength and self-control — for, after all, it is your life that continues here, and it's no good wasting it for what, on reflection, isn't much better than self-pity or indulgence in weakness.
There's not much point in trying to convince you (and others) how excessively you loved someone after they're gone. If your own stance towards them was consciously appreciative, you know how much you loved them; and if that love could manifest itself in any outwardly discernible behavior, it could have done so only while they were here. You can't gather affection points, as it were, in retrospect. (Neither before yourself nor in the eyes of others.) And obviously, you will remember them as long as you live — not just as long as you grieve. In fact, keeping someone in loving memory does not require you to be intensely distressed. (If it did, your loved one, if they loved you likewise, would probably have wished not to be remembered at all, don't you think?) Quite the contrary: if anything, a loving memory should be a positive one, one that appreciates all the goodness in your relationship, and its value. As soon as you can save that value from being eclipsed by emotions of grief, you'll give your love a more appropriate tribute. Take care.