half-life 1 ending

Q- I played half-life 1 and got all the way to the last boss (the big baby looking thing) and was never able to beat it. after about 2 weeks of trying, I gave up and never thought about it again. until today when I got half-life 2, it starts with the same skinny dude in the suit as in the first. I remember hearing that he gives u some options at the end of half-life 1, but I never knew. can someone tell me what happens after u kill the last boss and what the man tells u so that I can better understand the beginning of this game? Thank u very much.

A – Well, after you beat that big ass boss. Gman will take you to a tram. Though it is a much different tram since it can hyperspace or was it a normal tram? Never mind. Anyway, Gman asks you to join him. If you join you will live. But if you won’t. Gman will take you back to Xen where you’ll be slaughtered by thousand of Aliens.

P.S. Why don’t you use cheats? so you can finish HL1?