Quick Question about cheating in marriage (long, but please read)

I'm a poster here already but for reasons you'll see chose to post this question over an anonymous name.

I am only 16, but still post here on a regular basis. I don't care what you think.

Here's the situation:

From ages 0-13, I've seen my dad as almost the perfect dad. He's wasn't perfect in every way, but whenever I heard about divorces I just thanked God for blessing my parents with such a good relationship. I thought my parents had one of the best relationships in the world and literally thought there was a 0.0% of divorce in their relationship, it was that good.

Fast forward to April 04. My dad starts spending more time on the basement computer. I don't care though, I trust him for everything. Whenever I come down I ALWAYS saw him minimizing a window, every single time. I natrually got a little suspicious, since I was 14 and I guess getting smarter. Two years before that I had found a porn magazine in my dad's briefcase. Doesn't sound big at all, but from ages 5-12 I could never imagine my dad looking at porn or thinking about any other woman except my mom. Ok, I'm rambling now.

Anyways, after about 2 months of this suspicious [censored] I go on the downstairs computer and get some brillaint idea. I open word and press Paste. Don't know why, but I did. Up comes a huge conversation between my dad and another woman, having cyber sex. I starting crying on the spot and couldn't stop for an hour. I was so mortified I didn't know what to do. There was no one I could talk to about this. I was only 14 and I knew if I told my dad our relationship (which I cherished so much) would take a huge hit. I finally decided to print out the conversation and put it in an envelope and give it to my mom. Only possible choice, IMO. She reacts susprisingly well. She was obviously pissed and couldn't believe it, but my dad came and talked to me and told me he has had stress at work (he had already been talking about that constantly) and it all came together and he starting talking to another girl.

Two days later, he left his email account open, and I saw all the messages between my dad and this girl from the last 2 months. He had called her from work, that just broke my heart right away. Anyways, I'm tired of writing about this.

Did my dad deserve to be forgiven? I had taken notice that my perception of my parent's marriage has suffered since then, but it may have been bad before but since that happened I just noticed it more. It should be noted, that if my parents ever divorced it would break my heart and I wouldn't be able to handle it. I'm almost crying just thinking about divorce and that whole situation almost 2 years later. It almost makes me sick that if I heard about this in another marriage I would think the dad was total scum, but I don't know what to think about my dad. FWIW, this hasn't been brought up in my family in the last 9 months or so and only once or twice since June-ish 04. Also, I have a younger sibling and an older sibling, neither of them know about this situation. I would imagine if they were told they would be on the brink of hating my dad, and right now they love him and think nothing is wrong with my parents marriage, which I find sickening that both siblings think the marriage is still great. Also, is this kind of cheating any less worse than regular cheating, talk about that.

I'm just looking for some guidance. I don't know what I'm expecting in these answers. Seriously, keep the [censored] bullshit out of this thread, this issue is real important to me. Thanks if you got this far.