This plot I've thought of was inspired Crisis Novastar's removed fic Dark seduction, Moshking's Life of a Dragon: die for metal, and Enclave2277's Rarest of them all. What do they have in common? Twilight and Rarity have been seeing eachother behind Spike's back.
Twilight was secretly dating Rarity behind Spike's back for a few years. And the only ones who knew were maybe the princesses or no pony at all. Spike finds out during one of the special occasions, which he wasn't invited to again. The truth left betrayed, devastated, and beyond heart-broken. He runs back home and prepares to start packing to leave Twilight and the others and leave ponyville or possibly equestria forever, but his friends (the 4 remainders of the many 6) Applejack, Rainbow Dash, Fluttershy and Pinkie Pie manage to stop him. They reveal to him that they didn't know what was going on and try to persuade him not to go. Spike doesn't believe them due to his embittered heart and still tries to leave. Out of sympathy, desperation and fear of losing him forever, the girls prove their loyalty by having him stay with each of them for a while to give him time to get his head together and help mend his broken heart. And to make the promise legit they all pinkie promise not to tell Twilight or Rarity where he is until he's ready to talk to them. This way they can also sort out this whole mess with their friends, despite their anger toward how Twilight and Rarity treated him. As each of them take their turns looking after spike, their quality time reveals to each of them how much spike means to them. The reminisce how he impacted their live and begin to see more than just a friend in him
Meanwhile, Twilight and Rarity were fairing no better than Spike. Thier guilt and devestaion for how spike reacted and his choice words broke their hearts as well......more than any pony realizes. In fact, their relationship wasn't the only secret they kept from spike. For not everything is what it seems. In fact it was only half the truth. While Twilight and rarity have found in one another, there was also one other who have stolen their hearts. And weren't ready to reveal their secret to him until he was old enough.

How will this all play out? Will Spike's faith in his friends be restored and find something more than friendship? Or will his heartbreak and bitterness overtake him and leave equestria forever?
It will be up for you to decided. This sort of plot was never finished in any of these stories and i hope to find satisfaction and closure with the help of any creative writing mind to take this idea.

I will be posting more inspirational ideas for more writers through out all my joins groups and hopefully have a response.