Real Love is not supposed to be "pain" It's supposed to feel like a relief. Like you finally found your person and you can rest and the universe makes sense now.
So obviously, you have lost the one you love. Then, that makes a LOT of sense. But I wouldn't call that love anymore. It's simply defined as "heartbreak".
Trying to become perfect for someone is the opposite of real love. Real love accepts you for EXACTLY who you are and loves the things that you don't even like about yourself. Real love fixes your insecurities and makes you feel WHOLE and alive.
Hopefully that helps a tad bit more with the confusion. You'll know when it matches these things. Real love heals. It doesn't destroy. Real love is natural and NEVER forced.
Anything that destroys or is forced is NOT love. Of course there can be pain from real love if you lose a loved one, but even then you are left with a TRUE peace for having found something so special in this world.