Personally, these ultimate questions seem to me beside the point: heat death of the universe, big crunch, what difference does it make? This might happen to the universe, but it is not going to happen to any conscious being (by the time heat death occurs, life will not have occurred for millions of years--no energy flow to sustain it).
Consider this: you live in a house, or apartment, or whatever now, right? If you learned that it was going to be bulldozed tomorrow, you would be upset, because tomorrow you will have the problem of how to get on in life without a house. That would suck.
But this is probably not the first house (etc.) you have lived in--so now go back and think about those places. Maybe some have been torn down or bulldozed, or you could imagine that they have. How bothered are you? There might be one or two precious houses you remember for personal reasons, but chances are you generally accept that such things come to an end at some point, even if it's a bit sad.
Why don't you argue that if your current and/or previous houses don't last forever, then what is the point in living in any house? Why not despair of the finitude of temporary houses?
Because (I suggest) this line of thought forces you to think about the point of living in a house in more everyday terms. Even if every house you ever lived in has been destroyed, the reason you live in the house you do now is that it provides a good base to go out and get on with life. You can keep stuff there, you can hide there, you can get shelter there. That's why you live in a house. It's got nothing to do with the ultimate fate of houses.
I imagine the relevant application of this line of reason is obvious. If we lived in a universe where we had to spend all our time dodging gamma rays, it would make sense to ask "why the hell are we living here?" but only if there was somewhere else to go. But we don't live there, we live in a basically comfy place (as the universe goes) with the leisure of wondering about what it all means. It may not last forever, but you aren't going to live here forever anyway.
This doesn't address all the why? questions about life, the universe and everything. But being able to ask a question doesn't force the universe to cough up an answer. And worrying about the answer to a question with no answer is futile. So ask yourself, can I really expect an answer to these questions? What kind of universe would I have to live in for there to be answer to all the questions?
Religion comes up, as it usually does. But the 'answer' given by believers is usually worse than no answer. Why? Because God has a plan. Oh, great--so what does the plan say? Well, no one knows really, but God loves us and we are sure he has a plan for us. But why am I here, why now? God knows, but he wants you to figure it out for yourself, by living. But I tried figuring it out and I got stuck on the heat death of the universe! Can't I at least get a hint? Now the reply branches in a bunch of different ways: a) Don't make selfish demands of god! b) God did tell you, but you weren't listening. c) You'll understand eventually if you believe and just keep living. d) You'll know for sure when you stop sinning. None of these is any better than avoiding admitting ignorance.
But even if believers gave you a specific answer and could describe a reasonable plan, it might not help you anyway. If there is a divine plan, it is full of billions of moving parts---some are big important cogs, some are much smaller, less important cogs. It might be exciting to be one of the big cogs, but what are your chances? Mostly likely, you are a tiny cog in the plan, exactly like millions of others, that will turn till it breaks and be ground to nothing. Was that really what you had in mind? Would that answer to your "why?" help?
So I guess my suggestion would be to try thinking more practically or more concretely. Imagine whatever universe ending you can think of, and then ask, what does that actually say about my individual life? If you don't just jump to despair, you will see that it is a big stretch to think it says anything about your individual life, or even the whole human species. So turn your attention to your individual life: most things don't matter much to you, but a few things matter very much to you--family, friends, pets, school, job, career, etc. And when you ask, "what does it all matter?" remember to also ask "why isn't 'it matters to me' a good enough answer?" There might not be any other answer.
