It is a lot easier to prove that you don't love someone than it is to prove that you do, but one of the best 'proofs' I know is the desire to devote time to the person with no expectation of any sort of compensation, including gratitude, in return.
If we want proof of God's love for us, then we must look first at the Cross where God offered up His Son as a sacrifice for our sins. Calvary is the one objective, absolute, irrefutable proof of God's love for us.
Love is indescribable and unconditional. I could tell you a thousand things that it is not, but not one that it is. Either you have it or you haven't; there's no proof of it.
...God's love is so real that He created you to prove it.
I always see people tweeting about these crazy amazing things their boyfriend or girlfriend did for them. You shouldn't have to constantly be trying to prove your love when you're in a relationship.
How could I think the brief years were enough To prove the reality of endless love?
I'll grant the random access to my heart, Thoul't tell me all the constants of thy love; And so we two shall all love's lemmas prove And in our bound partition never part.
